MSP430FW42x ScanIF Demo Box Hardware/Software ... ScanIF Demo Box Hardware/Software Description

Application ReportSLAA578–April 2013

MSP430FW42x ScanIF Demo Box Hardware and SoftwareDescription

Zack Mak ........................................................................................................ Smart Grid Applications

ABSTRACT

This application report describes the specific information of the demo box that detects the disc rotationusing Scan Interface in MSP430FW42x. Both hardware and software are covered to help the developerunderstand the working principle of this demo box in a short time.

This document is based on Rotation Detection With the MSP430 Scan Interface (SLAA222). Detailedtechnical information can be found in that document.

Contents1 The Demo Box .............................................................................................................. 22 Demo Source Code ......................................................................................................... 33 References ................................................................................................................. 12Appendix A Schematic ......................................................................................................... 13

List of Figures

1 Demo Box .................................................................................................................... 2

2 The LCD...................................................................................................................... 3

3 Graphical Illustration for the Criteria of Updating SIFCNT1 ........................................................... 6

4 Relationship Between the Excitation Level, the DAC Level and SIFxOUT.......................................... 8

5 Value of SIFxOUT at the Same Excitation Level With Different DAC Value........................................ 8

6 Startup Calibration Flowchart.............................................................................................. 9

7 Coarse to Fine Calibration for System Startup ........................................................................ 10

8 Relationship Between Different Parameters ........................................................................... 11

9 Example of Run Time Calibration When Excitation Level Became Higher ........................................ 12

10 Simplified Schematic of the Demo Box................................................................................. 13

List of Tables

1 Pin Connection .............................................................................................................. 3

2 ScanIF Initialization ......................................................................................................... 3

3 TSM Setup ................................................................................................................... 5

4 State Table Setting of the Demo Source Code ......................................................................... 7

All trademarks are the property of their respective owners.

1SLAA578–April 2013 MSP430FW42x ScanIF Demo Box Hardware and Software DescriptionSubmit Documentation Feedback

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LCD displaycounter

Resister ladderfor LCD

Resister ladderfor LCD

Target boardMSP-TS430PM64

External jumperfor current

measurement

LC sensorPCB

LC sensorsunderneathLC sensorsunderneath

Rotatingdisc

The Demo Box www.ti.com

1 The Demo Box

Figure 1 shows different parts of the demo box. The target demo board is equipped with anMSP430FW429 for ScanIF operation.

Figure 1. Demo Box

NOTE:• To power the board, short the external jumper or connect the JTAG to the FET tool.• To measure the current consumption (using battery power), connect the external jumper

pin to a multi-meter.• The JTAG and the battery share the same VCC. Do not power the board using the JTAG

and the battery at the same time.• For the demo source code once the board is powered up, the LCD shows “CAL” for

initialization. If there is nothing shown on the LCD, there may be some bad contactsbetween the MCU and the target board. Opening and closing the cover of the MCUsocket should solve the problem.

• The LCD takes roughly 3 µA. Disconnect the LCD resister ladder to eliminate thatcurrent consumption. Of course, the LCD will not display numbers anymore.

1.1 LCD

The LCD layout is shown in Figure 2. Only the 3 digits on the left (A1, A2 and A3) are used and only thecorresponding pins are connected to the MCU.

2 MSP430FW42x ScanIF Demo Box Hardware and Software Description SLAA578–April 2013Submit Documentation Feedback


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R TX RXPM

5.00

5.004.0

92.5

9

1 22

2344

8.6

0

6.0

2

0.5

4

5.0°

0.13

3.82

0.7

7

5.0° 0.19

5.460.77

0.7

7

(1

(2

) 1

) 2ANT

PIN 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

COM0 A1M A1D AIDP A1P A2M A2D A2DP A2P A3M A3D A3DP A3P A4M A4D A4DP A4P A5M A5D A5DP A5P A6M A6D

COM1 A1G A1C A1N A1K A2G A2C A2N A2K A3G A3C A3N A3K A4G A4C A4N A4K A5G A5C A5N A5K A6G A6C

COM2 A1F A1B NEG A1J A2F A2B A2C0L A2J A3F A3B ANT A3J A4F A4B A4C0L A4J A5F A6B DEG A5J A6F A6B

COM3 A1E A1A A1Q A1B A2E A2A A2Q A2H A3E A3A A3Q A3H A4E A4A A4Q A4H A5E A5A A5Q A5H A6E A6A

PIN 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

COM0 RX A6P C0M0 BATT [] D4D D4DP D3D D3DP D2D D2DP D1D DC0L DNEG U PN PNE ) 2 TMR2

COM1 A6N A6K C0M1 B2 B1 D4C D4G D3C D3G D2C D2G D1C D1G REC R PE PSE ) 1 TMR1

COM2 TX A6J C0M2 B4 B3 D4B D4F D3B D3F D2B D2F D1B D1F PM D PS PSW (2 HRT

COM3 A6Q A6H C0M3 B6 B5 D4A D4E D3A D3E D2A D2E D1A D1E ALM L PW PNW (1 !

www.ti.com Demo Source Code

Figure 2. The LCD

Table 1. Pin Connection

LCD 1 2 5 6 9 10 25 26 27 28

MSP430F S6 S7 S8 S9 S10 S11 COM3 COM2 COM1 COM0W42x

2 Demo Source Code

The source code is divided into 3 files: lcd.c, main.c and scanif.c. This section focuses on the operation ofrotation detection using ScanIF only.

2.1 ScanIF Initialization

The initialization code is modified from Rotation Detection With the MSP430 Scan Interface (SLAA222).The main difference is that the demo source code adds test cycle settings for calibration. The setting isshown in Table 2. Some unrelated parameters are not shown.

Table 2. ScanIF Initialization

Register Setting Bitwise Value Meaning

SIFCTL2 = 0x0150; SIFDACON = 0 DAC is controlled by TSM

SIFCAON = 0 Comparator is controlled by TSM

SIFCAINV = 0 Comparator output is non-inverted

SIFCAX = 0 Comparator input from SIFCHx

SIFVSS = 0 Sample capacitor is grounded to SIFVss

SIFVCC2 = 1 AVcc/2 on

SIFSH = 0 Sample and hold disabled

SIFEN = 1 Excitation circuitry is enabled

SIFTCH1x = 01 Test channel 1 is mapped to SIFCH1

SIFTCH0x = 00 Test channel 0 is mapped to SIFCH0



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Demo Source Code www.ti.com

Table 2. ScanIF Initialization (continued)

Register Setting Bitwise Value Meaning

SIFCTL3 = 0x4000; SIFS2x = 01 SIF1OUT is the S2 source

SIFS1x = 00 SIF0OUT is the S1 source

SIFIS1x = 00 SIFIFG3 is set with each count, up or down, of SIFCNT1

SIFCTL4 = 0x33D0; SIFCNT1ENM = 1 SIFCNT1 decrement is enabled

SIFCNT1ENP = 1 SIFCNT1 increment is enabled

SIFQ7EN = 0 Q7 is not used to determine next PSM state

SIFQ6EN = 0 Q6 is not used to determine next PSM state

SIFDIV3Bx = 111 TSM restart after 330 ACLK cycle. At 32768Hz, that would be0.01sec. This reflects the sampling rate of the LC sensor.SIFDIV3Ax = 101

SIFCTL5 = 0x0045; SIFTSMRP = 0 Each TSM sequence is triggered by ACLK divider

SIFCLKFQx = 1000 Internal oscillator frequency = Nominal

SIFFNOM = 1 Internal oscillator frequency = 1MHz

SIFCLKEN = 1 TSM high frequency clock source = internal oscillator



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2.2 TSM Setup

The SIFTSMx is modified from the Rotation Detection With the MSP430 Scan Interface (SLAA222) sourcecode for calibration. The setting is shown in Table 3.

Table 3. TSM Setup

SIFTSM0 = 0x8800 All off. Idle for 18xSMCLK

(SIFTSM1 – 4: settings for SIFCH0) SIFCHx = 00

SIFTESTS1 = 0 (Test cycle uses SIFDACR6 for DAC)

SIFLCEN = 1 (LC enabled)

SIFCLKON = 1 (Hi-Freq clock on)

SIFTSM1 = 0x002C LC excitation for 1xSIFCLK

SIFEX = 1 (Excitation)

SIFTSM2 = 0x0424 Wait for 1xACLK

SIFACLK = 1 (use ACLK)

SIFTSM3 = 0x6934 Enable AFE for 14xSIFCLK

SIFREPEATx = 13

SIFDAC = 1 (DAC on)

SIFCA = 1 (Comparator on)

SIFTSM4 = 0x2174 Measurement for 5xSIFCLK

SIFREPEATx = 4

SIFDAC = 1

SIFRSON = 1 (Enable output latch) SIFCA = 1

(SIFTSM5 – 8: settings for SIFCH1) SIFCHx = 01

SIFTESTS1 = 1 (Test cycle uses SIFDACR7 for DAC)

SIFLCEN = 1 (LC enabled)

SIFCLKON = 1 (Hi-Freq clock on)

SIFTSM5 = 0x00AD LC excitation for 1xSIFCLK

SIFEX = 1 (Excitation)

SIFTSM6 = 0x04A5 Wait for 1xACLK

SIFACLK = 1 (use ACLK)

SIFTSM7 = 0x69B5 Enable AFE for 14xSIFCLK

SIFREPEATx = 13

SIFDAC = 1 (DAC on)

SIFCA = 1 (Comparator on)

SIFTSM8 = 0x21F5 Measurement for 5xSIFCLK

SIFREPEATx = 4

SIFDAC = 1

SIFRSON = 1 (Enable output latch)

SIFCA = 1

SIFTSM9 = 0x0200 SIFSTOP = 1 (End of TSM sequence)



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Suggested: +1

Suggested: –1,App note table 3: –1,

App note table 3: +1

10 00

0111

00


2.3 PSM Table Design

Rotation Detection With the MSP430 Scan Interface (SLAA222) points out that the 16-state table causes abouncing problem and suggested a 32-state table. However, if the 16-state table is carefully designed, thebouncing problem can be solved so that the PSM table can be kept simple.

Figure 3. Graphical Illustration for the Criteria of Updating SIFCNT1

From Figure 3, imagine the blue circle is the rotating disc for rotation measurement. The arrow on the bluecircle shows the rotating position. When that arrow is lying on any quadrates, the SCANIF gets the specificsensor state. For example, when the arrow lies on the yellow quadrate, S2 = 1 and S1 = 0. (State 10).

The arrows outside the square shows the different increment and decrement criteria based on twoimplementations: the implementation in Rotation Detection With the MSP430 Scan Interface (SLAA222)and the suggested implementation. The pointing direction of the arrows refers to the direction where thedisc is rotating and that state change updates the SIFCNT1 value. For example, suggested: + 1 meanswhen the disc rotates from state 10 to state 00, the SIFCNT1 will be +1.

It shows that in the application report implementation, the increment and the decrement of the counter isdone on different disc position. For the Quadrature Transitions for 2-Sensor Implementation table inRotation Detection With the MSP430 Scan Interface (SLAA222), if the disc rotates back and forth between00 and 01, the state change of 00->01 increases the counter by 1. But it will not decrease by 1 when thestate changes from 01 to 00. That will cause only +1 in this situation, which is the bouncing problem on16- state table stated in Rotation Detection With the MSP430 Scan Interface (SLAA222).

To solve that problem, set the increment and the decrement on the same position. In order to design thestate table, pair up the previous state and the current state, so that the increment and the decrement canbe occurred at the same position.



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Table 4 shows the state table setting of the demo source code.

Table 4. State Table Setting of the Demo Source Code

Look Up Previous CurrentPosition State State State Table Value Next

(Offset by LookCurrent Q2 Q1 Binary Byte Up MovingS1 S2) Q3 Q0 S1 S2 Q6 Q3 Q0 (-1) (+1) (Q6 ...Q0) Code Position Direction

NoP0 0 0 0 0 0 0 0 0 0 000 0000 0x00 P0 movement

Turn0 0 0 1 0 0 1 0 0 000 0001 0x01 P1 Right

Turn0 0 1 0 0 1 0 1 0 000 1100 0x0C P2 Left (-1)

Error0 0 1 1 1 1 1 0 0 100 1001 0x49 P3 (Opposite)

TurnP1 0 1 0 0 0 0 0 0 0 000 0000 0x00 P0 Left

No0 1 0 1 0 0 1 0 0 000 0001 0x01 P1 movement


Turn0 1 1 1 0 1 1 0 0 000 1001 0x09 P3 Right

TurnP2 1 0 0 0 0 0 0 0 1 000 0010 0x02 P0 Right (+1)


No1 0 1 0 0 1 0 0 0 000 1000 0x08 P2 movement

Turn1 0 1 1 0 1 1 0 0 000 1001 0x09 P3 Left

ErrorP3 1 1 0 0 1 0 0 0 0 100 0000 0x40 P0 (Opposite)

Turn1 1 0 1 0 0 1 0 0 000 0001 0x01 P1 Left

Turn1 1 1 0 0 1 0 0 0 000 1000 0x08 P2 Right

No1 1 1 1 0 1 1 0 0 000 1001 0x09 P3 movement

2.4 Calibration

The demo source code consists of two different calibration codes. One is for system initialization and oneis for run time calibration. The basic principle of both calibration codes are the same.

Figure 4 and Figure 5 show the relationship between the LC excitation level, the DAC value, and themeasured output SIFxOUT. The SIFxOUT is the comparator output of the DAC and the LC excitation.When the LC excitation stays at a certain level, if the DAC value is above the excitation level (DAC value1), the SIFxOUT becomes 0. If the DAC value is below the excitation level (DAC value 2), the SIFxOUTbecomes 1.

Based on this relationship, the MCU can find the excitation level (threshold value) by adjusting the DACvalue and check the SIFxOUT. For rotation detection, there are two excitation levels: with and withoutmetal covers the LC sensors. The excitation level is lower when there is metal covers the LC sensors andit is higher when there is no metal covers the LC sensors.



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DAC Value

DAC

Value1

Threshold

Value

DAC

Value2

SIFxOUT = 0

SIFxOUT = 1

LC

Excitation

Level

Analo

g Input M

ultip

lexer

To Timer_A

ExcitS/H

DAC 10 Bitw/ RAM1 2/

AVCC

Analog Front–End(AFE)

Scan I/F

SIFCI

SIFCI3SIFCI2

SIFCI1SIFCI0

SIFCH3SIFCH2

SIFCH1

SIFCH0

SIFVSS

SIFCOM

LC excitationlevel

SIFxOUT

DAC outputlevel

ProcessingState Machine

(PSM)

TimingState Machine

(TSM)

w/ oscillator

InterruptRequest

RotationData

ACLK

SMCLK


Figure 4. Relationship Between the Excitation Level, the DAC Level and SIFxOUT

Figure 5. Value of SIFxOUT at the Same Excitation Level With Different DAC Value

2.4.1 System Initial Calibration

When the system starts up, there is no reference for the LC excitation levels. If there is no predefinedvalue, it is not able to determine whether or not the LC sensor is covered by metal. In this situation, thesystem should find out the excitation level of those two states.

After the ScanIF setup, it sets different DAC values to SIFDACR(0-4) and check the SIFxOUT on eachsampling cycle. The calibration starts from coarse step size to fine step size in order to minimize thenumber of iteration. The calibration step is shown in Figure 6.



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Start measurement

No change in state.Keep increasing

DAC value

No change in state.Keep decreasing

DAC value

Change in state.Reducing Step SizeChange searching

direction

Change in state.Reducing Step Size by Half

Change searchingdirection

00

01

10

No

Yes

Initial DAC value (0x200)Initial Step size

Last StateSIFxOUT?

1

MeasuredStste of

SIFxOUT?

MeasuredStste of

SIFxOUT?

Is Step size smallenough?

Excitationlevel found


Figure 6. Startup Calibration Flowchart



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Excitation Level

Test DAC Value

SIFxOUT = 0

SIFxOUT = 1

Iteration

DA

C V

alu

e640

624

608

592

576

560

544

528

512

1 2 3 4 5 6 7 8 9 10


Figure 7. Coarse to Fine Calibration for System Startup

The threshold is continuously found. The maximum and the minimum value are recorded. When the discrotates, the MCU eventually finds the thresholds of two states. The two states are determined by thedifference (separation) of the maximum and the minimum value. If the difference is large enough, it is saidthat the two states are found. The final DAC value, SIFDACR0/2 and SIFDACR1/3 are calculated byaveraging the upper and the lower threshold, plus hysteresis.

After the calibration is done, the sampling rate can be lowered by modifying SIFCTL4 in order to lower thepower consumption.



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DAC Value Excitation Level

SIFxOUT = 0

SIFxOUT = 1

Uncovered

Covered by metal

Hysteresis

Hysteresis

Separa

tion

Rotation position

ThresholdValue (upper)

FinalSIFDACR0/2

FinalSIFDACR1/3

ThresholdValue (lower)

Averagedthreshold value


Figure 8. Relationship Between Different Parameters

2.4.2 Run Time Calibration

When the system runs, the calibration is done by using test cycle insertion (TCI) method. The TCImechanism is built inside the ScanIF module. It inserts test cycles between normal cycles that allows foreasy integration of calibration to occur without impacting the normal measurement cycle.

The TCI method uses SIFDACR6/7 for DAC output and SIFTCHxOUT for the measured result. It makessure that the testing process will not affect the normal operation.

In the demo code, it starts searching for upper threshold by setting the testing DAC value SIFDAC6/7 tothe stored upper threshold. It inserts test cycle and gets the SIFTCHxOUT for SIFDAC6/7. WhenSIFxOUT is 1, it also checks SIFTCHxOUT. If SIFTCHxOUT is 0, it shows that the excitation level becamelower. So SIFDAC6/7 decreases and the test is done again, until SIFTCHxOUT becomes 1. Alternately, ifSIFTCHxOUT is 1, it means that the excitation became higher. So SIFDAC6/7 increases and the test isdone again, until SIFTCHxOUT becomes 0. The final SIFDAC6/7 is the new upper threshold. The sameaction is then being done for lower threshold by setting the initial SIFDAC6/7 to the stored lower thresholdand by checking the SIFTCHxOUT when SIFxOUT is 0.

Once the new upper and the lower threshold have been found, the averaged threshold can be updated.



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DAC Value

NewThreshold

Old ThresholdInitial SIFDAC6/7

SIFxOUT = 0

SIFCHxOUT = 1

LC Excitation LevelSIFxOUT = 0: search for lower thresholdSIFxOUT = 1: search for upper threshold

References www.ti.com

Figure 9. Example of Run Time Calibration When Excitation Level Became Higher

3 References

Rotation Detection With the MSP430 Scan Interface (SLAA222)



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Appendix A Schematic

Figure 10. Simplified Schematic of the Demo Box



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MSP430FW42x ScanIF Demo Box Hardware/Software ... ScanIF Demo Box Hardware/Software Description