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Sample Laboratory Report #1

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This web page presents a sample report [Herwald, 1999]written in a microprocessor laboratory course at Virginia Tech.

In this report, carets (>) are given to reveal the line spacings in

the report's format (in an actual report, these carets would not

appear). Also, in this report, the actual appendices are not

complete (in an actual report, these appendices would be

complete, and each would begin on a separate page).

Moreover, an aspect of format that is probably not reflected by

your browser is that the report's title and appendices' titles are

in 14-point type, the subheadings and text are in 12-point type,

and the figure captions are in 10-point type.

Note that instructors of other laboratory courses may have

different expectations as far as the format and style of lab

reports in their classes. For instance, the guidelines for many

laboratory reports call foran abstract to appear in the report's

beginning. Moreover, some instructors frown on the use of the

first person (Iorwe).

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Design ofa Temperature Measurement and Display System

Using the 68HC11 Microcontroller>

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Introduction

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This report presents a design of a temperature measurement and display system that

incorporated the Motorola 68HC11 microcontroller, simply referred to here as the

HC11. This design was a valuable experience because similar temperature measurement

and display systems often are used in buildings and vehicles [Spasov, 1996]. The design

presented in this report made use of the HC11's analog-to-digital (A/D) converter and

the serial subsystems. As shown in Figure 1, the design included a temperature sensor

connected to one of the HC11's A/D input pins on Port E, and light emitting diodes

(LEDs) connected to Port B. These LEDs acted as temperature indicators. Additionally,

the design included a connection between the HC11 and a remote personal computer

(PC). This connection served to send messages regarding temperature to the PC. An

assembly software program developed for this design performed various functions for

using the added hardware.
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temperature. Included in this objective was the task of connecting the temperature sensor

and the LEDs to the HC11. Also included in this objective was the task of designing

software to do the following: initialize the A/D converter and serial subsystems; control

the measurement and storage of temperature in a RAM variable called TEMP; and

control the display of temperature on the LED outputs. The second objective of the

design was to use the HC11 to indicate if the temperature went outside of prescribed

limits: below 20 degrees Fahrenheit or above 90 degrees Fahrenheit. Included in this

objective was the task of connecting the HC11 to a remote PC terminal through an RS-

232 connection. Another task within this objective was developing software to initialize

the serial subsystem. The final task of this objective was to create subroutines for the

software program of the first objective to have the HC11 send a message to the PC if the

measured temperature went outside the stated limits.

This report first presents the procedures for and assessment of the design to have the

HC11 measure temperature. Then the report discusses the procedures for and

assessment of adding a serial output to the HC11 design to communicate whether the

temperature is outside of prescribed limits.

Figure 1. Temperature measurement and display system developed for the Motorolla

68HC11 microcontroller, which is attached to a universal evaluation board (EVBU).

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Connecting a Temperature Measurement Circuit to the HC11

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Connecting a temperature measurement circuit to the HC11 microcontroller involved

both hardware and software. Hardware was added to control the measurement and

display of the temperature. Software served to control this added hardware. In

performing the testing and design for this part of the project, my laboratory partner and I

divided the work in the following way. My partner assumed the lead role in connecting

the hardware, and I assumed the lead role in writing the programs. Although one of us

had a lead role in performing either the hardware or the software, we worked

collaboratively in checking both the hardware and software and in troubleshooting any


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problems.

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Procedures for Design. The hardware for the temperature measurement circuit included

both a temperature sensor attached to Port E and LEDs attached to Port B. The circuit,

which is shown in Figure A-1 of Appendix A, was designed according to the

specifications obtained from the Computer Engineering Laboratories web site for ECPE

4535 [Lineberry, 2001].

Within the circuit was an LM3911 temperature controller integrated circuit (IC), theoutput of which we connected to a non-inverting op-amp. The output of this op-amp

attached to the HC11 A/D input pin E2 through a 1000-ohm resistor. The circuitry was

scaled so that 0 volts out corresponded to 0 degrees and 5 volts out corresponded to

110 degrees. To each of the output pins of Port B, we connected LEDs using a

74HC244 buffer IC and 330-ohm current limiting resistors, all of which are shown in

Figure A-1. The LEDs were located in the breadboard area of the trainer kits.

To control this added hardware, we programmed the HC11 following the pseudo code

and program listing given in Appendices B and C, respectively. The program shown in

Appendix C consisted of three subroutines that were called from the main program

(Main). The three subroutines were named Startup, GetTemp, and SetDisp. The Startupsubroutine was used to enable the A/D converter subsystem. First the A/D charge pump

was powered up by setting bit 7 of the Option register. Then, bit 6 was cleared so that

the charge pump used the system E-clock [Spasov, 1996]. After a 100 microsecond

delay to allow the charge pump to stabilize, the control word $22 was written to the

ADCTL register to start continuous, single-scan conversions on pin E2 of Port E.

The subroutine GetTemp was used to input and scale the analog voltage from the

temperature sensor circuit. The register ADR3 held the result of the A/D conversions,

which was treated as an 8-bit binary fraction between 0 and 1. This value was loaded

into accumulator A and then multiplied by a scale factor of 110 using the MULinstruction. The result of this multiplication was a 16-bit number between 0 and 110, with

an 8-bit integer portion stored in accumulator A and an 8-bit fractional portion stored in

accumulator B. The integer portion of the temperature was then stored in the RAM

variable TEMP.

The subroutine SetDisp controlled the lighting of the LEDs connected to Port B. The

amount of lighting was based on the present value of TEMP. First, TEMP was loaded

into accumulator A and compared with the value 20, the designated cut-off for low

temperature. Accumulator B was cleared to zero and represented the initial value to be

written to Port B. If the value in accumulator A was greater than or equal to 20, then thevalue in accumulator B was shifted one position left and incremented, and 10 was

subtracted from accumulator A. The process then repeated itself as long as the value in

accumulator A was greater than or equal to 20. An abbreviated form of this process

appears in Figure 2 (the complete process appears in Appendix C). After the number of

LEDs to turn on were determined, as shown in Figure 2, the number of bits indicated by

the count value in accumulator B were set high on Port B beginning with bit 0 [Motorola,

1991].


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Figure 2. Flowchart illustrating the determination of the number of Port B bits to

enable for the LED display.

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Assessment of Design. To test the operation of the GetTemp and SetDisp subroutines,

we measured the actual temperature with a temperature probe and compared that withthe measured value represented by the LED display indicators at several different

temperature settings. Table 1 shows the results of the measurement comparison, where

the actual temperatures measured are shown on the left, and the temperatures

represented by the number of LEDs lit are shown on the right. From Table 1, we verified

that the developed hardware and software for this part of the lab were functioning

properly. Overall, this section of the laboratory went smoothly.

Table 1. Comparison of temperature measurements.

Actual Temperature Number of LEDs Lit

15F 0

28F 1

33F 2

56F 4

110F 8

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Adding Serial Output to the HC11

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This section presents the addition of four subroutines to the existing software developed

in the previous section. The added subroutines, listed in Appendix D, were called

InitSCI, SendChar, SendMsg, and CheckLimits. The InitSCI subroutine initialized the

serial subsystem of the HC11 so that it could communicate with the host PC at 9600

baud [Spasov, 1996]. This initialization was done by writing control words to the BAUD,

SCCR1, and SCCR2 control registers in the HC11 as shown in Appendix C.

In performing the testing and design for this part of the project, my laboratory partner and

I divided the work in the followin wa . M artner assumed the lead role in connectin


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the hardware, and I assumed the lead role in writing the programs. Although one of us

had a lead role in performing either the hardware or the software, we worked

collaboratively in checking both the hardware and software and in troubleshooting any

problems.

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Procedures for Design. The first subroutine, SendChar, was added to send a single

data byte from the HC11 to the remote PC terminal. The data byte to be sent was

contained in accumulator A. After waiting for the TDRE bit in the SCSR register to be

set, indicating that the HC11 is ready to transmit another byte, the value in accumulator Awas written to the SCDR register to begin the transmission [Motorola, 1991].

The second subroutine, SendMsg, used the SendChar subroutine to write character

strings to the remote PC terminal. Before calling SendMsg, the X index register was set

to point to the beginning of the character string to be sent. The SendMsg subroutine then

sent out the string by calling SendChar for each character until the NULL character was

reached, which marked the end of a string.

The third and final subroutine, CheckLimits, was added to the existing software program

to check the temperature range. The subroutine CheckLimits called SendMsg to print the

following message if TEMP was less than 20 degrees Fahrenheit: "Temperature is very

low." If TEMP was greater that 90 degrees Fahrenheit, CheckLimits called SendMsg to

print the following message: "Temperature is very high." If TEMP was between 20 and

90 degrees Farenheit, CheckLimits called SendMsg to print the following message:

"Temperature is acceptable." A flag variable called FLG ensured that the messages were

not repeatedly sent for each entry into the very hot, very cold, or acceptable temperature

regions. FLG was set to zero if TEMP was between 20 and 90 degrees, one if TEMP

was less than 20 degrees, and two if TEMP was greater than 90 degrees.

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Assessment of Design. While developing the design presented in this section, several

mistakes and difficulties were encountered. The initial setup of the serial subsystem of the68HC11 involved some troubleshooting. We also had problems with sending the alarm

messages more than one time because a flag variable was not set. The diagnosis and

solutions to these problems are discussed in this section.

Initially, the serial writes from the 68HC11 to the host PC did not work properly because

the SendChar routine did not check the TDRE bit before writing to the SCDR register.

This caused characters to be dropped when sending a message. We also had a problem

sending out messages using SendMsg because we did not terminate the message strings

correctly with the NULL zero. By adding the NULL zero to the end of the strings, the

sending of messages worked as expected.

A final problem was the output rate of the alarm messages. At first, we did not set a flag

to indicate to the program that a message had already been sent to the PC. This failure

caused messages to be continually sent to the PC terminal when the temperature was

outside of the normal operating region. This problem was fixed by making a variable

called FLG that was set as soon as the alarm message was sent and then cleared when

the temperature returned to the normal operating region.

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Conclusions

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This report has discussed the development of a temperature measurement and display

system. The objectives of this lab were to develop the necessary hardware and software

to have the HC11 measure temperature and indicate whether that temperature fell outside

of prescribed limits. Both objectives were met. By keeping track of the measured

temperature, the HC11 was able to control an LED temperature display. Also, if the

temperature became very cold or hot, the HC11 sent an alarm message to a host PC

terminal.

This lab has introduced us to the important topics of A/D conversion and serialcommunications. In the lab, an A/D converter allowed us access to analog inputs of

temperature from a remote computer. Besides temperature measurement, A/D converters

have many applications in automatic control systems and factory automation. For

example, in an electric motor drive, the phase currents and flux are continually measured

by using scaling circuitry and an A/D converter input to a microprocessor.

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>Appendix A: Hardware Schematic>

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Figure A-1 presents the hardware schematic for the temperature circuit. The circuit was

designed according to the specifications obtained from the Computer Engineering

Laboratories web site for ECPE 4535 [Lineberry, 2001].


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Figure A-1. Hardware schematic for the temperature measurement circuit designed for

this lab. In an actual report, all the connections, pin numbers, and pin labels should be

shown.

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Appendix B: Pseudocode for the Software Developed>

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XXXXXXXXXXXXXXXXXX*

XXXXXXXXXX

XXXXXXXXX

XXXXXXXXXXXXXXXXXXXXXX

XXXXXXXXXXXXXX

XXXXXXXXXXXX

XXXXXXXXXXXXXXXXXX

XXXXXXXXXX

XXXXXXXXX

XXXXXXXXXXXXXXXXXXXXXX

XXXXXXXXXXXXXX

XXXXXXXXXXXX

*In an actual report, the pseudocode would appear here. Also note that some professors allow you

to subs titute an appendixwith program flow charts for this appendix.

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Appendix C: Program Listing>

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Assembler release TER_2.0 version 2.09

(c) Motorola (free ware)

0001 ;**************************************************

0002 ; Temp_Monitor: This program implements a temperature

0003 ; measurement and display system. The A/D system is

0004 ; used to read an analog temperature. The value is

0005 ; scaled to Farenheit, and displayed on an LED bar

0006 ; display. If the temperature is above 90 or below
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0007 ; 20, a message is transmitted over the serial link.

0008 ; Programmer: JMB

0009 ;*************************************************

0010

0011 ; Define some I/O registers

0012 1004 PORTB EQU $1004

0013 102b BAUD EQU $102B

0014 102c SCCR1 EQU $102C

0015 102d SCCR2 EQU $102D

0016 102e SCSR EQU $102E

0017 102f SCDR EQU $102F

0018 1030 ADCTL EQU $1030

0019 1031 ADR1 EQU $1031

0020 1032 ADR2 EQU $1032

0021 1033 ADR3 EQU $1033

0022 1034 ADR4 EQU $1034

0023 1039 OPTION EQU $1039

0024

0025 ; Define some constants

0026 005a UPPER_LIMIT EQU 90 ; upper temperature limit

0027 0014 LOWER_LIMIT EQU 20 ; lower temperature limit

0028 0002 HOT EQU 2 ; flag value indicating

0029 ; temperature UPPER_LIMIT

0030 0001 COLD EQU 1 ; flag value indicating

0031 ; temperature < LOWER_LIMIT

0032 0000 OK EQU 0 ; flag value indicating

0033 ; temperature is within limits

0034 000d CR EQU $0D ; ASCII code for carraige return

0035 000a LF EQU $0A ; ASCII code for line feed

0036

0037 ; Variables


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0038 0100 ORG $100 ; place in RAM area

0039 0100 TEMP rmb 1 ; current temperature

0040 0101 FLAG rmb 1 ; flag indicating system sta

0041 ; (HOT, COLD, or OK)

0042

0043 b600 ORG $B600 ; EEPROM area

0044 ;***************************************************

0045 ; Temp_Monitor: This routine initializes the system, and

0046 ; then enters an endless loop. In this loop, it reads

0047 ; the current temperature, updates the LEDs, and then

0048 ; sends a message to the serial link, if necessary.

0049 ; Input: none

0050 ; Output: none

0051 ; Registers/variables modified: ACCA, ACCB, CCR, TEMP, FLAG

0052 ;****************************************************

0053 Temp_Monitor:

0054 b600 8e 01 ff lds #$1FF ; initialize stack pointer

0055 b603 bd b6 11 jsr Startup ; initialize A/D and SCI,

0056 ; initialize RAM variables

0057 Main:

0058 b606 bd b6 1d jsr GetTemp ; get current temperature

0059 b609 bd b6 29 jsr SetDisp ; update LED display

0060 b60c bd b6 3c jsr CheckLimits ; check upper and lower limits

0061 b60f 20 f5 bra Main ; repeat

0062

0063

0064

0065 ;****************************************************

0066 ; Startup: This routine initializes the system. It calls

0067 ; other routines to initialize the A/D system and the

0068 ; SCI system. It also initializes the FLAG variable.


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0069 ; Input: none

0070 ; Output: none

0071 ; Registers/variables modified: ACCA, IX, CCR, FLAG

0072 ;****************************************************

0073 Startup:

0074 b611 bd b6 7c jsr InitAD ; power up the A/D system

0075 b614 bd b6 a2 jsr InitSCI ; initialize the serial interface

0076

0077 b617 86 00 ldaa #OK ; initialize FLAG

0078 b619 b7 01 01 staa FLAG

0079

0080 b61c 39 rts

0081

0082 ;****************************************************

0083 ; GetTemp: This routine gets the current temperature.

0084 ; It reads the A/D value, converts it to Farenheit,

0085 ; and stores the result in TEMP. An A/D value of $00

0086 ; corresponds to 0 degrees, and $FF (actually $100)

0087 ; is 110 degrees, so the A/D value is multiplied by

0088 ; 110 to convert to temperature.

0089 ; Input: none

0090 ; Output: New temperature stored in TEMP

0091 ; Registers/variables modified: ACCA, ACCB, CCR, TEMP

0092 ;****************************************************

0093 GetTemp:

0094 b61d b6 10 31 ldaa ADR1 ; read A/D value

0095 b620 c6 6e ldab #110 ; multiply by 110

0096 b622 3d mul ; to get temperature

0097 b623 89 00 adca #$00 ; round to 8 bits

0098

0099 b625 b7 01 00 staa TEMP ; store new temperature


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0100

0101 b628 39 rts

0102

0103 ;****************************************************

0104 ; SetDisp: This routine updates the LEDs to display

0105 ; the current temperature. The LEDs are arranged as a

0106 ; bar display with a range of 20 - 90 degrees, in 10

0107 ; degree steps. This routine determines how many of the

0108 ; LEDs should be turned on based on the current temperature.

0109 ; Input: TEMP variable

0110 ; Output: none

0111 ; Registers/variables modified: ACCA, ACCB, CCR

0112 ;****************************************************

0113 SetDisp:

0114 b629 c6 00 ldab #$00 ; all LEDs off initially

0115 b62b b6 01 00 ldaa TEMP ; get current temperature

0116

0117 SD_Loop:

0118 b62e 81 14 cmpa #20 ; is value 20?

0119 b630 25 06 blo Update_LEDs ; branch if not

0120 b632 58 lslb ; else, turn on next LED

0121 b633 5c incb

0122 b634 80 0a suba #10 ; value = value - 10

0123 b636 20 f6 bra SD_Loop ; repeat

0124

0125 Update_LEDs:

0126 b638 f7 10 04 stab PORTB ; update the LEDs

0127

0128 b63b 39 rts

0129

0130 ;****************************************************


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0131 ; CheckLimits: This routine checks to see if the current

0132 ; temperature is within the upper and lower limits. If

0133 ; not, then a warning message is transmitted over the

0134 ; serial link.

0135 ; Input: TEMP, FLAG

0136 ; Output: none

0137 ; Register/variables modified: ACCA, ACCB, IX, CCR

0138 ;****************************************************

0139 CheckLimits:

0140 b63c b6 01 00 ldaa TEMP ; get current temperature

0141 b63f 81 5a cmpa #UPPER_LIMIT ; temp upper limit?

0142 b641 23 12 bls Check_Lower ; branch if not

0143 b643 c6 02 ldab #HOT ; have we already sent a

0144 ; warning for this?

0145 b645 f1 01 01 cmpb FLAG ; (i.e., is FLAG == HOT?)

0146 b648 27 31 beq CL_Exit ; branch if so (don't repeat

0147 ; warning message)

0148 b64a f7 01 01 stab FLAG ; update flag

0149 b64d ce b6 e2 ldx #HOT_MSG ; send "hot" warning message

0150 b650 bd b6 c5 jsr SendMsg

0151 b653 20 26 bra CL_Exit ; and exit

0152

0153 Check_Lower:

0154 b655 81 14 cmpa #LOWER_LIMIT ; temp $102F

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References>


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Lineberry, Bob, "Computer Engineering Laboratories Website at Virginia Tech,"

http://www.ee.vt.edu/cel(Blacksburg, VA: ECE Department, 1998), ECpE 4535:

Laboratory Assignments, Lab X.

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Motorola Corporation,M68HC11 E Series: Reference Manual, rev. 3 (Oak Hill,

Texas: Motorola Corp. 1991), chapters 9 and 12.

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Spasov, Peter,Microcontroller Technology: The 68HC11, 2nd ed. (Englewood Cliffs,NJ: Prentice Hall, 1996), pp. 107, 355-359, 460.

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