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DURING project construction, manyhobbyists must have wondered ifthe reason their masterpiece wasn’t

working was due to a faulty i.c., or if thei.c. they’ve just removed from an old boardactually works. The project described hereprovides a simple way to quickly test theoperation of most TTL and CMOS digitali.c.s.

To explain how the Digital I.C. Tester

works, let’s examine the humble 7400 TTLNAND gate device as an example. Thedatasheet says the package contains fourlogic gates, each one having two inputsand one output, which behave according tothe truth table in Table 1.

Table 1. Truth table for a 2-inputNAND gate

Input 1 Input 2 Output

L L HL H HH L HH H L

To test the satisfactory functioning ofeach of the four gates in the i.c. package,each of the four input logic configurationsin Table 1 must be applied to each gate andthe resulting logic output levels recordedand compared against the expected results.

A profile for an i.c. to be tested is firstgenerated from the device’s datasheet.Within the profile, an instruction sequenceis specified that applies defined logic lev-els to the specified input pins, and recordsthe results generated on the output pins.

The actual results received are com-pared against those that are expected, andfrom this it is possible to ascertain if thei.c. is functioning correctly.

It should be noted that some i.c.s requirea great many individual logic operations totest them completely. For example, the7430 8-input NAND gate requires 256 sep-arate input logic level permutations to betested.

The complete circuit diagram for the

Digital I.C. Tester is shown in Fig.1. Whenpower is supplied to the board, it first pass-es through bridge rectifier REC1. If theinput supply input is a.c., REC1 converts itto d.c. If the input is already d.c. it ensuresthat the polarity is correct for IC1, whichthen regulates the voltage down to approx-imately 5V. Capacitors C1 to C4 plus C11provide smoothing.

A PIC16F877-20 microcontroller, des-ignated as IC3, is used as the core of thecircuit and is run at its maximum speed of20MHz, as defined by crystal X1. Sincethis design uses RS232 protocol to inter-face to a serial port on a PC, a voltage levelconverter is employed to convert the PIC’s5V logic levels to the ±12V levels requiredby the RS232 standard (many PCs do notactually require this higher voltage for ser-ial comms input and will accept +5V/0Vinputs. Ed).

This is accomplished by IC2, aMAX232 line driver. Capacitors C5 to C8

are used by IC2’s internal circuitry to con-vert the supplied voltage from 5V to ±12V.Connection to the PC is via a 9-pin femaleD-type connector, SK2.

To test the functionality of a digital logici.c., a known set of logic levels must bepresented on each pin and the resultingresponses received back from the i.c. thenanalysed.

The PIC16F877 has a total of 33 I/O

(input/output) pins. Of these, 24 are usedto connect the PIC to the i.c. under test.Each of the 24 I/O pins is connected to apin on the i.c. test socket (SK3) via a 100resistor, within resistor modules RM1 toRM3. These resistors act as current lim-iters to protect the PIC and the deviceunder test. The danger is that an output ofthe test i.c. could become connected to aPIC I/O pin also designated as an output.

Each pin on the i.c. test socket is biassedto the +5V test power rail via a 4k7 resis-tor (within resistor modules RM4 to RM6).This is to force unused pins on the testsocket to a known logic level, and alsoenables open collector TTL i.c.s that havetheir outputs either floating or pulled toground to be tested.

During the test cycle, the PIC sends alow logic level to the base of transistor

Everyday Practical Electronics, October 2002 717

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TR1 via resistor R3, which in turn appliespower to the i.c. under test, via either thepower patch pin (TP1) or via the dual-in-line (d.i.l.) switch module S1.

Transistor TR1 also supplies +5V to thecommon pins of the pull-up resistors withinmodules RM4 to RM6. As soon as testing iscomplete, TR1 is switched off automatical-ly, disconnecting power from the test i.c.Capacitor C12 provides smoothing of theswitched +5V rail from TR1.

With power applied to the board andTR1 off (non-test mode), the PIC’s RB6and RB7 pins are available to allow anexternal programmer access to the PIC.

It is expected that when in service the

project will be powered from a sealedplug-in mains power supply adaptor.Either an a.c. or d.c. power supply unit canbe used and the connections to the printedcircuit board (p.c.b.) are not polaritysensitive.

required. If a turned pin socket is not avail-able, two rows of turned pin socket stripscan be used instead.

Provision has been made on the p.c.b. toaccommodate two pairs of turned pinsocket strips, one pair of 10 pins (withinthe SK3 area), and one pair of 12 pins(TB2 and TB3) which may be used if it isdecided not to use a ZIF socket. Thisallows narrow i.c. packages of up to 20pins or the wider packages of up to 24 pinsto be tested. Though not as convenient as aZIF, this does make a cheaper option.

Power can be applied to the i.c. undertest either via the jumper patch pins (TP1and TP2), or predefined power configura-tions can be selected from the 4-way d.i.l.switch bank, S1. This switch allows aGND (0V) connection to be made to pin12 of the test socket and a +5V connectionto be made to pins 19, 20 and 22, as

718 Everyday Practical Electronics, October 2002

A power supply unit capable of supply-ing around 100mA and between 9V to 12Vshould be ideal. If the input voltageexceeds this, then it might be necessary tofit a larger heatsink to IC1. The prototypedraws approximately 30mA when instandby, rising when testing. The exactcurrent drawn will depend on the i.c. beingtested.

There are several possible choices for the

method that will be used to connect i.c.s tothe tester via socket SK3. The preferredmethod is a ZIF (Zero Insertion Force) sock-et. They are available in different sizes andformats but one should be chosen thataccepts i.c.s of up to 24 pins and differentpackage widths (a “universal” type).

The ZIF socket can be mounted directlyon the board, or a 24-pin turned socket canbe fitted first and then the ZIF pushedfirmly into that. This allows the ZIF to beeasily removed and used elsewhere if

b

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PIC16F877-20PIC3

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RB2

RB1

INT/RB0

RX/DT/RC7

TX/CK/RC6

SDO/RC5

SDI/SDA/RC4SCK/SCL/RC3

CCP1/RC2

T1OSI/CCP2/RC1

T1OSO/T1CKI/RC0

PSP7/RD7

PSP6/RD6

PSP5/RD5

PSP4/RD4

PSP3/RD3

PSP2/RD2PSP1/RD1

PSP0/RD0

GNDGND

+VE +VEMCLR

OSC2/CLKOUT

OSC1/CLKIN

RE2/AN7/CS

RE1/AN6/WR

RE0/AN5/RD

RA5/AN4/SS

RA4/TOCK1

RA3/AN3/VREF+

RA2/AN2/VREF-

RA1/AN1

RA0/AN0

C910p

C1010p

X120MHz

C1220µ

C2100n

REC1

IC17805

C3100n

C4220µ

C11100n

R1470Ω

D1

POWER

IN

COM

OUT +5V

RM44k7

R34k7

TP3 TP4

TP5TP6

R7470Ω

D4

R4 R52k2 2k2

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NC

COMMS

+5VON

NC

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CLK

DATA

MCLR

1N4148D2

R21k

+5V PATCH PIN

TP1

TR1BC213

R6470Ω

RM3100Ω

1 16

RM2100Ω

1 16

RM1100Ω

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+ +

a

a

a a

k

k

k k

D3

POWERIN

TEST *

*SEE TEXT

TB1

1

2

3

4

SK1

Fig.1. Complete circuit diagram for the Digital I.C. Tester.www.epem

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Everyday Practical Electronics, October 2002 719

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(SEE TEXT)SERIAL CABLE LINKS

TP10TP9

TP8TP7

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SK3

NC

NC

NC

NC

MAX232IC2

V+

V+

V

GND

R1 OUT R1 IN

T2 OUT

T1 OUT

R2 OUT R2 IN

T2 IN

T1 IN

C2

C2+

C1

C1+

C8

C5

C7

1µ

1µ

1µ

1µ

C6

4k7RM6

4k7RM5

+

+

+

++

**SEE TEXT

0V PATCH PIN

ResistorsR1, R6, R7 470 (3 off)R2 1kR3 4k7R4, R5 2k2 (2 off)RM1 to

RM3 100 8 xindividual resistors d.i.l.module (3 off)

RM4 toRM6 4k7 8 x commoned

resistors s.i.l. module(3 off)

All 0·25W 5% carbon film or better exceptRM1 to RM6.

CapacitorsC1, C4 220 radial elect. 25V

(2 off)C2, C3, C11 100n ceramic disc,

5mm pitch (3 off)

SeeSSHHOOPPTTAALLKKppaaggee

C5 to C8 1 radial elect. 50V(4 off)

C9, C10 10p ceramic disc, 5mmpitch (2 off)

C12 10 radial elect. 16V

SemiconductorsREC1 bridge rectifier 50V 1AD1, D3 green l.e.d., 3mm (2 off)D2 1N4148 signal diodeD4 red l.e.d., 3mmTR1 BC213 pnp transistor

(or similar)IC1 7805 +5V 1A voltage

regulatorIC2 MAX232 RS232 line

driverIC3 PIC16F877-20P

microcontroller,preprogrammed(see text)

MiscellaneousX1 20MHz crystalS1 4-way s.p.s.t. d.i.l. switch,

p.c.b. mounting (see text)

SK1 power connector(see text)

SK2 9-way D-type sub-min.connector, female, p.c.b. mounting

SK3 24-pin universal ZIFsocket (see text)

TB1 4-way terminal pinstrip

TB2, TB3 turned pin socket strip(2 x 12-way) (see text)

Printed circuit board, available from theEPE PCB Service, code 371; p.c.b.supports (4 off); 40-pin d.i.l. socket; 16-pind.i.l. socket (4 off); heatsink 21°C/W forIC1 and mounting hardware; solid insulat-ed wire for jumper links; solder, etc.

Approx. CostGuidance Only ££2255

excl. connectors

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720 Everyday Practical Electronics, October 2002

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ak

REC1

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D2

C2 C3

IC1

C1C4

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R6 R

7

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C10 X1

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RM3

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RM4

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a

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C11

IN

COM

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++ +

++

+

+

TP7 TP8

TP9 TP10

C12

6.05in (153.7mm)

4.02

5in

(102

. 2m

m)

R4

R5

*

*

*

*

*SEE TEXT

1234

371

Fig.2. Printed circuit board component layout and full size copper foil master track pattern.

DIGITAL I.C. TESTER CIRCUIT BOARD

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required. These combinations cater for themajority of 14, 16 and 20-pin packages.

Provision has been made on the p.c.b. toaccommodate an 8-way d.i.l. switch bankfor S1 if required instead of the 4-way(using the unused holes seen below S1 onthe p.c.b. in Fig.2). The additional fourways can be hard-wired to any combina-tions wanted. The p.c.b. tracks locatedbelow the switch should make the settingup of these combinations easy.

The Digital I.C. Tester is constructed on

a single-sided p.c.b. whose component lay-out and tracking details are shown in Fig.2.This board is available from the EPE PCBService, code 371.

It is recommended that good quality i.c.sockets are used for IC2, IC3 and the three100 resistor modules, RM1 to RM3.Assemble the board in any order you pre-fer, but preferably making the link-wireconnections first.

The two link wires located to the left ofSK2, the 9-pin RS232 connector (betweenTP7/TP8 and TP9/TP10), help determinewhich type of serial cable will be used, seeFig.3. If a straight-through serial cable is tobe used, pin 2 to pin 2, pin 3 to pin 3, thenthese links should be parallel to each otheras shown in Fig.3b.

If a cross-over serial cable is being used(pin 2 to pin 3 and pin 3 to pin 2 – as inFig.3a) then the links should be crossed asin Fig.3c. Place a small piece of sleevingover one of the link wires so that they donot short together.

Be careful to observe the correct polari-ty of the semiconductors, electrolyticcapacitors and l.e.d.s. It is also worthwhileorientating the i.c. sockets as shown, eventhough they are not actually “polarity con-scious” in the normal sense. Doing so helpsto ensure that the i.c.s. themselves areinserted the correct way round.

Do not insert IC2 and IC3, or connectthe tester to the PC, until preliminarychecks have been completed.

If the board is to be used as is (i.e. with-out a case), attaching small stick-on rubberfeet to each corner is a wise precaution. Ifthe intention is to house it in a suitablecase, a 24-pin wire-wrap type socket canbe used for SK3 as this will provide ade-quate clearance between the componentson the p.c.b. and the case lid. The ZIF sock-et can then be plugged into the wire-wrapsocket. A similar arrangement can be usedfor mounting d.i.l. switch S1.

No provision for a power socket wasmade on the p.c.b. due to the differenttypes of power connectors currently in use.Instead, two terminal pins can be fitted andthen an appropriate power socket for thechosen power supply soldered directly tothese, as in the prototype.

Note that there are three holes locatedaround IC1 that are not used. These pointsenable power to be tapped off for use withother circuits if desired.

There are four terminal pins (TP3 toTP6) located to the left of IC3. Ignore pinsTP3 and TP5. The TP4/TP6 pair controlthe RS232 interface rate. With the defaultPIC firmware and 20MHz crystal, connect-ing TP4 to TP6 selects an interface speedof 57·6K baud. Without this link, 19·2Kbaud is used. A plug-in jumper link wasused on the prototype.

Once construction is completed, re-

check that all components have beenoriented correctly and look for any soldersplashes or bridges that might haveoccurred during assembly. Using a multi-meter set to ohms, check the resistanceacross capacitor C4 to ensure that there isno short circuit. A brief reading may beobtained whilst C3 and C4 charge.

If all is OK, continue testing, otherwisedo not attempt to apply power until theproblem has been removed as IC1, thebridge rectifier or the power supply unitcould be damaged.

Making sure that the board is not restingon anything conductive, connect a suitable

power supply. Switch on the power andl.e.d. D1 should illuminate. Switching themultimeter to d.c. volts, measure the volt-age on pins 11 (+VE) and 31 (GND) of thesocket for IC3. A reading of approximately5V, within a few percent, should be seen.

If the 5V rail is not present or l.e.d. D1does not illuminate, carefully check aroundIC1 and IC3 for short circuits or dry joints,and check the polarity of the D1.

Switch off the power supply and discon-nect it from the mains supply when makingany changes to the board.

Once everything seems to be in order,insert IC2 and IC3, being careful of correctorientation and not to let any of the i.c. pinsbend under whilst being inserted. The PIC,IC3, can either be a preprogrammed ver-sion (see later) or if a suitable in-circuitprogrammer is available (Toolkit Mk3/TK3for instance), it can be programmed onboard via the TB1 connector.

Referring to Fig.1, resistor R2 and diodeD2 permit the correct use of the PIC’sMCLR pin 1 both during and afterprogramming.

The completed unit needs to be connect-ed to a suitable serial port on the PC. Thecable should have a 9-pin male connectoron one end for the unit and a suitable con-nector for the PC’s serial port on the other.Fig.3a shows a cable schematic for a com-puter having a 9-pin serial port connector.For this cable, the cable selector links onthe p.c.b. should be straight, as in Fig.3b(see earlier).

The PC software has been written inVisual Basic 6 (VB6) and should run onany recent Microsoft operating systemincluding Windows 95, 98, ME, NT 4.0,2000 and XP.

The installation set consists of four files:Setup.exe, which is the installation pro-gram, Setup.lst, which provides setup con-trol parameters to the Setup.exe, plusICTest1.cab and ICTest2.cab which con-tain the actual Digital I.C. Tester program,VB6 runtime files and i.c. model definition(type number) files.

Create a temporary new folder havingany name of your choice, e.g. C:\ICTester,and copy the files into it. Then run theSetup.exe either by enteringC:\ICTester\Setup.exe in the Windowsrun dialogue window or by double-clickingon Setup.exe in the File Explorer.

Once the setup has begun, most usersshould be able to accept the default settingsoffered. During the installation process,you may be asked to restart your computerif you have not previously installed theVisual Basic 6 runtime components or theyare out of date. Reboot the computer andrestart the setup process as required.

The temporary directory C:\ICTestercan be deleted if no longer required oncethe setup is complete. If running the instal-lation from the EPE CD-ROM, insert thedisk into the disk drive and run theSetup.exe program located on it, asdescribed above, then follow the prompts.

Once complete, the Setup program willcreate a new program group called DigitalI.C. Tester. You can find it be clicking the

Everyday Practical Electronics, October 2002 721

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RXTX TX

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STRAIGHT CABLE.PIN2 TO PIN 2 ANDPIN3 TO PIN3

CROSS-OVER CABLE.PIN2 TO PIN 3 ANDPIN3 TO PIN2

TP7

TP7

TP8

TP8

TP9

TP9

TP10

TP10

A)

B)

C)

Fig.3. Links to be made in respect ofserial lead type, see text.

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Start icon on the lower left hand side of themain Windows screen, and then selectingprograms. You should see it listed there.

Connect the serial cable and power sup-ply unit and switch on. The l.e.d. D1should illuminate. Also, to confirm that thePIC is running and executing its firmware,l.e.d. D4 should also illuminate.

Start the PC program running and youwill be presented with the main workingarea, similar to Photo 1.

By default, the PIC firmware and the PCsoftware are set to communicate at 19·2Kbaud (TP4/TP6 link excluded – seeearlier).

The PC software must be configured touse the COM port that you have connectedthe serial cable to. By default, the softwareuses COM:1. If you are not using COM:1,you can change this setting by selecting theTools menu and then Configuration, whichproduces a display such as in Photo 2. Ashort-cut is to click the spanner icon on thetoolbar.

From here, you can change settings thatcontrol communication, default displaycolours, directories or folder locations andsome other ad-hoc settings. Change theCOM port to the required setting and clickOK. All configuration changes are storedfor later use.

Next you need to test the actual commu-nication link between the PC and theDigital I.C. Tester. Again, select Tools fromthe top and this time select ConfirmCommunication Interface at the bottom ofthe menu.

A screen will be displayed detailingsome checks you should first make.When you are ready, click the Start but-ton. You will see some text scroll up inthe panel on the right hand side of thewindow and perhaps l.e.d. D4 flickeringon the tester.

The panel on the window will turn greenif the communications link is satisfactory.If it turns red this indicates that the com-puter cannot establish a communicationslink with the tester. Perform the checks asdetailed and try again. Most often the com-munications failure is due to the wrongCOM port being selected or an incorrectcable being used.

If all is well, you can now proceed to testan i.c., but note that if l.e.d. D4 illuminatesconstantly during the testing process, thisindicates a possible communications prob-lem. In which case check the serial cableand the PC software speed settings in theconfiguration window.

The software is supplied with profiles

for a selection of common TTL and CMOSdevices. For the following testing examplewe shall use a TTL 74LS00, a quad 2-inputNAND gate. To properly follow this dis-cussion now, it is best to have the PC soft-ware running.

Drop the i.c. to be tested into the testsocket, making sure that the bottom righthand pin of the i.c. is located in the bottomright hand pin of the socket.

Different i.c.s can have their power railpins located in different positions.Typically, the bottom left hand pin is GNDand the top right hand pin is +VE but thisis by no means always the case. The rowsof turned pin sockets alongside the testsocket can be used to route power to thecorrect pins, but more on this in a moment.

Next, you need to tell the PC softwarewhich i.c. type is going to be tested. To dothis, you need to load a profile file that relatesto the specified type. This file contains detailsabout the number of pins on the i.c., whichpins are inputs and outputs, have no internalconnection and which are its power pins.

The profile also contains detailed instruc-tions on how to test the i.c. From the pro-gram’s main menu select File and then LoadIC Profile. After a few moments, a list of theavailable profiles should be displayed in theright hand panel (see Photo 3).

If the panel is empty then you will needto tell the software where the “Datasheets”folder is located. The default isc:\Program Files\ICTester\DataSheets.The left hand panel allows you to browseyour computer’s drives and folders untilyou locate the “Datasheets” folder.

Scroll down the list of available profilesand select “7400”. You can double-click toload or click once and then click the Loadbutton. The Profile Directory windowshould now disappear and you will see justthe main application window. On the statusbar at the bottom, though, you should nowsee some additional information, such asthat in Photo 4.

To start the testing process, select IC

Test from the top menu and then select TestSpecified IC. A window similar to that inPhoto 5 will be displayed.

There are four main areas to this win-dow. The Start and Stop buttons are used tobegin and terminate the testing processaccordingly. The Performance panel isused to get additional information dis-played during the testing process.

If Update Pin Display has a check markdisplayed, a representation of the i.c. beingtested will be displayed on the screen. Asthe logic levels change on the actual devicebeing tested, they will be reflected on thisdisplay (this is useful when the Single Stepoption is also selected).

The function Update Logic Trace willrecord a trace similar to a storage oscillo-scope that can be studied after the testingprocess has been completed. Enabling theReal-time Plot option will keep the traceupdated as the testing progresses instead ofjust displaying the results at the end of thetest.

These options, if selected, will impacton the performance of slower PCs. To getthe best possible speed, do not enable theseoptions. However, for now, enable all threeso you can see exactly what happens.

The Test Mode panel controls how thetesting is performed. Normally, Single Testwould be selected. If you suspect that adevice has an intermittent problem,though, you can set the software to do aContinuous Test. The test-cycle will thenbe repeated up to 999 times.

Abort On Error will terminate the testingcycle if any error is detected in the i.c.

Single Step is useful if, for example, youwant to probe around the i.c. under test

722 Everyday Practical Electronics, October 2002

Photo 1. Main working area toolbar onPC screen.

Photo 2. Serial communications con-figuration screen.

Photo 3. Selection screen for i.c. types.

Photo 4. Status bar.

Photo 5. The “testing” screen.

Photo 6. Pin connections dialoguescreen.

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with an oscilloscope or logic probe. Everytime a pattern is sent to the test i.c., the PCsoftware will display a message box askingyou to press the <CR> (<ENTER>) keybefore it moves onto the next step.

The Test Statistics panel shows howmany test cycles have been made (0 to999), the current sequence or pattern num-ber being executed as specified in thedevice profile file, and how many test-cycles the device has passed or failed.

When ready, click the Start button.

Because this is the first time you have test-ed an i.c. with this power pin configuration,a dialogue box is displayed (see Photo 6).The picture shows how to correctly applypower to the i.c. under test. Also, it showsyou how the i.c. should be inserted in thesocket.

Notice that in this case, no power patchwires are required as this i.c. package issupported by the on-board d.i.l. switches.So, set d.i.l. switches S1/3 and S1/4 to theON position, as indicated.

Press OK to start the test. All being well,after a couple of seconds you should havea display similar to that in Photo 7.

Select Window from the top menu andthen Tile Vertically to get the software toarrange everything neatly for you on thescreen.

In the case of the i.c. represented inPhoto 7, it actually failed during the testingprocess. The right hand panel shows thatthe problem occurred with patternsequences 0007 and 0008. Sequence 0007shows what the Digital IC Tester sent to thei.c. Sequence 0008 shows what the deviceprofile says should be the response fromthe i.c. The next line shows what theresponse from the i.c. actually is. An “X”means Don’t Care about the logic level.

Whilst this is helpful, it is not too clearexactly what the problem is. The trace onthe left hand side of the screen shows thelogic levels present on each pin of the i.c.during the test. The trace is updated aftereach Read operation is performed.

The display has four yellow traces whichare the outputs of each of the four NANDgates. Since they should all behave thesame, it’s quite clear that there is a problemwith the gate whose output is on pin 11. Insome cases, though, the actual problemmight not be clear, especially if the i.c.only contains one or two gate arrays. If youselect Diff on the Pin Logic Trace, the tracedisplay will change and look similar to thatin Photo 8.

The dotted line indicates what the pro-file is expecting back as a response fromthe i.c. under test. As can be seen with pin

11, the logic level dropped from high tolow before it was expected. Anotheroption available is GND, located directlyunder the Diff option. Enabling GNDforces a dotted line showing where thelow logic level for each pin would be onthe display. This makes a useful traceseparator when the screen starts lookingcrowded.

Since the number of i.c. devices on the

market is constantly changing, the testerwould soon become obsolete if the user didnot have the ability to add new profiles asrequired. To create a new profile, selectCreate IC Profile on the main Tools menu,see Photo 9.

You will need to enter the i.c.’s typenumber and a brief description about thedevice. Next select how many pins thedevice has, and specify which pins are des-ignated as inputs, outputs, power or haveno internal connection. You do this by

repeatedly clicking on each pin in theusage column. Additionally, you can createshort tags (descriptions) for each pin,which are displayed along with the pinnumbers on the Logic Trace screen. Whenready, click the Next button.

You must now tell the Tester what logic

levels to send to the i.c. and what theexpected results will be (see Photo 10).

To test a 7400 quad 2-input NAND gate,for example, 10 instructions are required:

Sequence 1 – Reset. This sends a Resetcommand to the PIC and should always beincluded unless there is a specific reasonnot to. You can include as many Reset com-mands as required and at any location with-in the script.

Sequence 2 – +VE On. This switcheson the +5V supply to the i.c. under test. Italso applies +5V via transistor TR1 to thethree commons of the pull-up s.i.l. resistormodules, RM4 to RM6.

Sequence 3 – Send. Here, we are send-ing low logic levels to pins 1, 2, 4, 5, 9, 10,12 and 13. These pins were defined on theprevious screen as inputs. You can onlysend logic levels to pins defined as inputs.

Everyday Practical Electronics, October 2002 723

Photo 8. Test screen in “difference”highlighting mode.

Photo 7.Typical screen display during testing, on this occasion showing that the i.c.is faulty (see text).

Photo 10. Creating an i.c. test proce-dure profile.

Photo 9. Creating an i.c. pin functionprofile.

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Sequence 4 – Read. We now read backthe logic levels from the i.c. being tested.We expect pins 1, 2, 4, 5, 9, 10, 12 and 13to be low since we have set them low inthe previous instruction. However, wemust now indicate which logic levels areexpected on each output pin. Accordingto the truth table we looked at for aNAND gate earlier, all gates shouldreturn a high logic level. We now contin-ue sending logic levels to the i.c. beingtested and then reading back the actuallogic levels from it.

There is no need to send a Config com-mand in the above sequence since the PCsoftware sends the required configurationbased on the profile information you spec-ified on the first screen during the profilecreation.

Some i.c.s, however, have pins that can be

either an input or an output, depending onthe logic level of some other pins, and the74245 is an example of this (see Photo 11).

At Sequence 7, a Config command hasbeen inserted. This enables the tester to bereconfigured and specify which pins areinputs or outputs. Testing resumes fromSequence 8.

Select the Reset command and click AddInstruction. A new line will be added to thedisplay. Do the same for +VE On. Next,insert a Send command. This is the binarypattern we want to present to the i.c. undertest. Logic levels are changed by clickingthe cell on the new line that you want tochange.

Normally, after a Send command, youwill perform a Read. But this is not alwaysthe case. For the Read, you can specify thata pin designated as an output should haveeither a High or Low logic level or that itdoesn’t matter (“X”).

Once the required instructions have beencreated, press OK to save the profile.

The up and down arrow buttons allowlines to be moved up and down in the exe-cution order. The Delete Line button allowsinstruction lines to be removed from theprofile.

The configuration options can be select-ed from the main menu and are located

under Tools, Configuration (see Photo 2earlier). When selected, there are fivegroups of configuration settings that can bechanged.

The first group deals with the serialinterface characteristics. The COM portand interface speed are changed here. Atthe bottom of the screen there is a TimingAdjustment button. In certain circum-stances, it is possible to under-run the PC’sserial buffer. Increasing this value forcesthe PC software to wait longer for incom-ing data, the drawback being that the soft-ware will run slightly slower.

To check that this setting is correct,insert a known good i.c. into the tester andset for continuous testing. If after thedefault 999 tests no failures have beenreported then the setting is correct. If anyfailures are detected then this value shouldbe increased by a value of 1 and the testperformed again.

The next group allows the informationdisplay colours to be changed. Clickingany of the coloured panels brings up thecolour picker dialogue.

The Paths groups allows the defaultlocation of the Data Models (i.c. types)storage path to be specified. Clicking theellipsis button on the right (the onewith . . .) allows you to explore the avail-able disk drives and folders and locate thelocation of the data model files.

The settings groups allow some displayoptions and the DIP switch type and usageto be specified. The Show Tool Bar andShow Status Bar options allow the Tooland Status bars to be shown or hidden,which is useful if screen real estate isscarce.

In some cases, the software attempts togain the user’s attention by flashing mes-sages on the screen. The option AllowFlashing Text controls whether these mes-sages flash or are static.

The option Always Warn About Test ICPower Pin Configuration controls how thesoftware warns the operator about the powerpin configuration of the i.c. under test. IfOn, the software always issues a warning. IfOff, the software only issues a warningwhen either the first i.c. of the session is tobe tested or a new i.c. type has been select-ed that has a different power configurationfrom the previous type tested.

The DIP Type options control the lookof the graphic used for showing the d.i.l.

switch settings. Select the type that bestmatches your d.i.l. switch type. The switchbank size defaults to 4-Way. If this ischanged to 8-Way, indicating that you haveopted to fit the 8-way switch for S1, theSetup DIPS (“DIPS” referring to the othername, dual-in-line-package, by which d.i.l.switches are sometimes known) button willbe enabled.

Selecting Setup DIPS allows you tospecify how you have wired the additionalfour switches.

The printer icon allows a template to beprinted that contains all the texts requiredto label the Digital I.C. Tester. Also, a cus-tom legend is printed that can be affixednext to the d.i.l. switch S1.

All configuration options are saved andautomatically used the next time the PCsoftware is started.

It is worth noting that, in most cases,holding the mouse pointer over a control orbutton will provide some additional infor-mation on its use.

An additional feature was added to thesoftware to experiment with displayinglogic states for i.c.s running in-circuit onother p.c.b.s, and this has been left in thepublished software for reader’s own exper-imentation purposes (see Photo 12).

A test connector, consisting of an i.c. testclip, connected to a piece of ribbon cableand terminated with a 24-pin i.c. headerplug, allows the Digital I.C. Tester to beconnected to the in-circuit i.c. Once con-nected the Logic Analyser function can beselected from the Tools menu.

The Logic Analyser monitors andreports the logic levels on between 1 and

Photo 11. Example of a profile screen being set for multiple function pins.

Photo 12. Logic analyser experimentalscreen.

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24 pins. The pins to be monitored areselected in the Monitor Pins panel. Anoptional trigger pattern can be specified ifrequired. A “tick” indicates a high logicstate and the absence of a tick indicates alow logic state. When all monitored pinshave the specified trigger pattern, theAnalyser is triggered.

There are two primary modes of operationfor the Analyser. The mode Only DetectPattern Changes displays each new logic pat-tern as it changes. Free Running grabs thelogic levels as fast as possible. If FreeRunning is selected, an optional delay can bespecified from 0 to 9999ms between eachsample being made. Update Pin Display andLogic Display work as previously discussed.The Activate Device Pull-Ups controlswhether the s.i.l. pull-up resistor modules(RM4 to RM6) have their common connec-tions powered or not.

When the logic analyser starts, itinstructs the PIC to “grab” logic level sta-tus information as fast as possible andtransmit this to the PC. The PC thenattempts to process and display this infor-mation. Because of this, the analyser hasseveral practical limitations.

Firstly, due to the hardware design and

the way the PIC operates internally, thePIC’s I/O ports are read at slightly differenttimes. This means that when changinglogic levels are trying to be captured, thereis a possibility of inconsistent or unexpect-ed results being displayed.

Also, no matter what settings youselect, the PIC frantically transfers dataas fast as it can to the PC and does notstore any of the results internally. Thismeans that the capture speed is limited tothe maximum speed of the serial inter-face, making it quite slow in relation totoday’s computer speeds.

The Digital I.C. Tester has successfully

tested a variety of i.c.s without any prob-lem, including 74, 74F, 74LS, 74HC andCMOS 4000 series. The only slight excep-tion to this was with the HC series. Theserefused to test correctly with the originalprototype which used 330 buffer resistormodules (RM1 to RM3). These wereswapped for 100 ones, as specified forthis published version, and then the offend-ing i.c.s tested fine.

The design aims to give a go/no-go logicreport on the i.c. being tested. It is beyond

the scope of the tester to attempt to measurethe i.c.’s analogue operational parametersand compare them with its technical specifi-cation. Perhaps when a PIC is available with24 onboard analogue-to-digital converters,the author will revisit the design.

The author would like to thank his brother

Peter for supplying a large selection of “testsubjects”, most of which looked like theybelong in the Science Museum!

All software for this project is available

for free download from the EPE ftp site, oron CD-ROM (for which a charge applies)from the EPE Editorial office, see the EPEPCB Service page for details. The PIC pro-gram software is supplied in MPASM for-mat (.ASM and .HEX). See this month’sShoptalk page for details of obtaining pre-programmed PICs.

The datasheet for the MAX232 is avail-able from the Maxim website atwww.maxim-ic.com.

Datasheets for the majority of TTL i.c.scan be found on Texas Instruments website at www.ti.com.

Everyday Practical Electronics, October 2002 725

EPE Bounty Treasurer HunterLooking down the components list for the EPE Bounty

Treasure Hunter, there is nothing in the way of electroniccomponents that should need a treasure hunter to find them!Although the author preferred to use the SGS-ThomsonHCF40106, in an application such as this any hex Schmittinverter having the code 40106 in its identity will perform thejob. Ignore the prefix, that’s only the manufacturer’s code. Byand large, with any digital logic i.c., it’s only the number itselfwhich is important, not the manufacturer. Make sure, ofcourse, that the device is one having normal pins that go intoa p.c.b., and is not a surface mount device.

The hardware may present you with a bit more of a searchrequirement, this is where your large local DIY stores comein handy – and you enjoy browsing those anyway, don’t you!

I.C. TesterOnce again, there are no components that are unusual in

the I.C. Tester, with the possible exception of the MAX232RS-232 line driver. If your favourite stockist doesn’t have it,we know that ESR do, their advert is on page 706. It is alsostocked by Maplin, code number FD92A, they describe it asan RS-232 Transmitter-Receiver (same thing as an RS-232line driver). Tel: 0870 264 6000. Web: www.maplin.co.uk.

It’s worth shopping around for the ZIF socket as these canvary considerably in price between sources (quality-wise, ofcourse, you get what you pay for!). See later for details ofobtaining the software. Pre-programmed PICs are obtain-able from EPE advertisers Magenta Electronics ( 01283565435, web: www.magenta2000.co.uk), price £10 each(overseas add £1 p&p).

Headset CommunicatorIt’s the TDA7052 that your local stockist may not have for

the Headset Communicator, even though he is likely to haveall the other components, which are common-place. Againwe know that Maplin (see above) stock it, code UK79L(ignore the 1W power amp module that they also call theTDA7052).

Regarding the connectors, yes, they can seem a bitexpensive, but quality is well worth paying for in this contextand XLRs are the preferred connectors used byprofessionals in the audio world. Try ESR for these – their

advertisement is on page 706 – they also stock theTDA7052 i.c. If funds permit, buying ready-made XLR con-nection leads could provide greater reliability – a fact whichmay well be appreciated in the type of situation in which thisunit is intended to be used.

PIC-Pocket BattleshipsExcept for one item, all components in the PIC-Pocket

Battleships project are perfectly standard, which we expectany supplier to keep in stock. This fun game uses a PICmicrocontroller, but it is not one that appears frequently inEPE projects. It is the PIC16C54, which is one of the earlierPICs (long before the ’84 etc) and which is not electricallyerasable, requiring exposure to UV light to do so through awindow set into the device. This PIC is available pre-pro-grammed only from the author, Bart Trepak, 20 The Avenue,London W13 8PH. It costs £5.50 inclusive (overseas add £1for P&P), payment made out to B. Trepak, and only in £ ster-ling and drawn on a British Bank, although UK postal ordersare accepted.

Software is available separately as stated below. Note thatToolkit TK3 is not designed for use with PIC16C54 devices.

Printed Circuit Boards and SoftwareApart from Battleships, which is built on stripboard, this

month’s projects all have p.c.b.s. Their code numbers arequoted in the respective Components Lists and are availableas stated on the EPE PCB Service page (page 763).

All the software required is available for free downloadfrom our ftp site. The easiest access route to this is via themain web page at www.epemag.wimborne.co.uk – usethe click link at the top saying “FTP Site (Downloads)”, thenclick on PUB, then on PICS, and then look for the appropri-ately named folder.

Software is also available on disk from the Editorial office.Battleships is on EPE Disk 5, but the I.C. Tester is on its ownCD-ROM. To order these disks, see the EPE PCB Servicepage, which also gives their prices.

That’s it for now, Dave will be back with you next month.

PLEASE TAKE NOTEIngenuity Unlimited (July 2002)The locations of VR1 and R1 in the Car Battery TrickleCharger (page 487) should be reversed, so that R1 isplaced between the output and adjustment, and VR1between adjustment and ground.

with John Becker

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