SHIFTIN SHIFTOUT timing problem

Does anyone know how to lengthen (slow down) the LOW period of the SHIFT clock?
The statement

Code:

DEFINE SHIFT_PAUSEUS 2

extends the HIGH period of the shift clock to about 10 uS but the LOW period remains fixed at about 2 uS. I need to retain something close to a 50:50 duty cycle but at a lower speed with about 10 uS HIGH and 10 uS LOW.

Cheers
Brian

I've dealt with this two ways, manually modify the shiftin/out library adding nop's in assembler to create a delay, or a better option is to bit bang the routines manually. This way you have complete control of the timing. Examples here

http://www.melabs.com/resources/samples/pbc/shift.bas

bit banging for less than 8 bits

Thanks for that Steve.

I had considered the bit bang approach and had found the BS2 routines on the Melabs site. I am using the Intersema pressure transducer which needs the SHIFTOUT value\bits option to clock out some 2 and 3 bit values as well as regular 8 bit bytes. I guess I'll just have to bite the bullet and dive into the assembler. The lazy option is not going to cut it.

Cheers
Brian

Hey Brian,

No need to use assembler depending upon yout timing requirements. You can insert pauses in the routines to meet your requirements. This also can makes it easy to read and write different numbers of bits.

bit banging the Intersema sensor

I could not make the PBP ShiftIn or ShiftOut routines work reliably with the latest Intersema MS5541C although the same code had worked a treat for several years. Intersema must have made some internal changes, one at least to reduce power consumption when MClk stops, or maybe meLabs has tweaked some code.

Intersema show DIn must be stable before SClk goes high. ShiftOut in PBP shows this as Mode 0. In the direction from Intersema to PIC, ShiftIn mode 2 should get the sense and timing right according to the PBP and Intersema waveform sketches. The problem seems to be that neither Intersema nor PBP specifies the setup time between data change and clock strobe. On an oscilloscope the clock follows data by a few hundred of nanoseconds which ought to be enough but I get many bad reads with the potted ShiftIn and ShiftOut routines.

I hand coded the 7 commands from PIC to Intersema and the single reply code from Intersema to PIC. The code is none too elegant but it now works 100% every time. Previously I was getting about 75% mis-reads of pressure data and some DA5541C chips would not work at all.

Code:

OutShift: for fa = 1 to clockbits 'OutShift adds an extra bit at the end din = (1 & iword) 'select lowest bit & pauseus 1 'will actually be 4 uS or so sclk = 1 : pauseus 1 : sclk = 0 iword = iword >> 1 'get next LSB, clock out zeros after 16 bits next fa sclk = 1 : pauseus 1 : sclk = 0 'extra clock per DA5541B_00513 page 13 return ResetIntersema: ' resets ALL pressure sensors ' shiftout din, sclk, 0, [85, 85, 0\5] ' Sense of Din is IN to 5541 output din : output sclk clockbits = 20 : iword = %0101010101010101 '16 bit data word gosub outshift return ConvertDelay: ' specific to each sensor if tank = 0 then While dout0 = 1 wend endif if tank = 1 then While dout1 = 1 wend endif if tank = 2 then While dout2 = 1 wend endif return FetchWord: ' read specific channel reply input dout0 : input dout1 : input dout2 : output sclk : iword = 0 if tank = 0 then for fa = 15 to 0 step -1 'need 17 clock bits so add one at end sclk = 1 : pauseus 1 'wait for Intersema to present next bit iword.0[fa] = dout0 'read the bit on selected channel sclk = 0 'drop clock next fa 'do it 16 times endif if tank = 1 then for fa = 15 to 0 step -1 'need 17 clock bits so add one at end sclk = 1 : pauseus 1 'wait for Intersema to present next bit iword.0[fa] = dout1 'read the bit sclk = 0 'drop clock next fa 'do it 16 times endif if tank = 2 then for fa = 15 to 0 step -1 'need 17 clock bits so add one at end sclk = 1 : pauseus 1 'wait for Intersema to present next bit iword.0[fa] = dout2 'read the bit sclk = 0 'drop clock next fa 'do it 16 times endif sclk = 1 : pauseus 1 : sclk = 0 ' 17th clock bit ii = iword.byte0 : ij = iword.byte1 return ReadFactoryCal: ' This unpacks the factory calibration coefficients from the just ' read W1 ~ W4. ' These bitmaps are unpacked into the 6 working coefficients ' C1 to C6 which are then stored in EEROM for later use. 'W1 gosub resetintersema ' shiftout din, sclk, 0, [87, 1\5] ' Send W1 pattern to all sensors clockbits = 12 : iword = %000101010111 'request W1 pattern gosub outshift gosub fetchword ' recall selected Tank reply W1.byte0 = ii W1.byte1 = ij if (w1 = 0) or (w1 = 65535) then debug "W1 error", 13, 10 goto readfactorycal endif 'W2 gosub resetintersema ' shiftout din, sclk, 0, [215, 0\5] ' Send W2 pattern clockbits = 12 : iword = %000011010111 gosub outshift gosub fetchword W2.byte0 = ii W2.byte1 = ij if (w2 = 0) or (w2 = 65535) then debug "W2 error", 13, 10 goto readfactorycal endif 'W3 gosub resetintersema ' shiftout din, sclk, 0, [55, 1\5] ' Send W3 pattern clockbits = 12 : iword = %000100110111 gosub outshift gosub fetchword W3.byte0 = ii W3.byte1 = ij if (w3 = 0) or (w3 = 65535) then debug "W3 error", 13, 10 goto readfactorycal endif 'W4 gosub resetintersema ' shiftout din, sclk, 0, [183, 0\5] ' Send W4 pattern clockbits = 12 : iword = %000010110111 gosub outshift gosub fetchword W4.byte0 = ii W4.byte1 = ij if (w4 = 0) or (w4 = 65535) then debug "W4 error", 13, 10 goto readfactorycal endif CalcCoefficients: ' this serves all three sensors. 'C1 C1 = W1 >> 3 'unpack coefficient read (108 + tank*20), z.byte0 'store read (109 + tank*20), z.byte1 if z<>c1 then write (108 + tank*20), c1.byte0 'store write (109 + tank*20), c1.byte1 endif 'C2 C2 = ((W1 & %0000000000000111) << 10) + (W2 >> 6) read (110 + tank*20), z.byte0 read (111 + tank*20), z.byte1 if z<>c2 then write (110 + tank*20), c2.byte0 write (111 + tank*20), c2.byte1 endif 'C3 C3 = W3 >> 6 read (112 + tank*20), z.byte0 read (113 + tank*20), z.byte1 if z<>c3 then write (112 + tank*20), c3.byte0 write (113 + tank*20), c3.byte1 endif 'C4 C4 = W4 >> 7 read (114 + tank*20), z.byte0 read (115 + tank*20), z.byte1 if z<>c4 then write (114 + tank*20), c4.byte0 write (115 + tank*20), c4.byte1 endif 'C5 C5 = ((W2 & %0000000000111111) << 6) + (W3 & %0000000000111111) read (116 + tank*20), z.byte0 read (116 + tank*20), z.byte0 if z<>c5 then write (117 + tank*20), c5.byte1 write (117 + tank*20), c5.byte1 endif 'C6 C6 = W4 & %0000000001111111 read (118 + tank*20), z if z<>c6 then write (118 + tank*20), c6 endif Show5541Coefficients: 'only used during diagnostics ' high txd : pause 1 ' debug 13, 10, "Tank #", #tank, ", W1 = ", #w1, ", W2 = ",_ ' #w2, ", W3 = ", #w3, ", W4 = ", #w4, 13, 10 ' debug "Derived coeffs C1 = ", #C1, ", C2 = ", #C2, ", C3 = ",_ ' #C3, ", C4 = ", #c4, ", C5 = ", #C5, ", C6 = ", #C6, 13, 10 return ReadTank: ' D1 is Pressure - D2 is Temperature. Same code for all 3. 'MUST know Tank# before calling this routine. 'D1 gosub resetintersema ' shiftout din, sclk, 0, [47, 0\5] ' Select D1 pattern clockbits = 11 : iword = %00000101111 gosub outshift gosub convertdelay gosub fetchword d1.byte0 = ii d1.byte1 = ij if (d1 = 0) or (d1 = 65535) then debug "D1 error", 13, 10 goto readtank endif 'D2 gosub resetintersema 'shiftout din, sclk, 0, [79, 0\5] ' Select D2 pattern clockbits = 11 : iword = %00001001111 gosub outshift gosub convertdelay gosub fetchword D2.byte0 = ii D2.byte1 = ij if (d2 = 0) or (d2 = 65535) then debug "Tank ", #tank, ", D2 error", 13, 10 goto readtank endif CalcTempPress: read (108 + tank*20), c1.byte0 read (109 + tank*20), c1.byte1 read (110 + tank*20), c2.byte0 read (111 + tank*20), c2.byte1 read (112 + tank*20), c3.byte0 read (113 + tank*20), c3.byte1 read (114 + tank*20), c4.byte0 read (115 + tank*20), c4.byte1 read (116 + tank*20), c5.byte0 read (117 + tank*20), c5.byte1 read (118 + tank*20), c6 ut1 = 8*c5 + 10000 dt = d2 - ut1 if dt < 0 then dt2 = dt - (dt*dt)/(128*64) else dt2 = dt - (dt*dt)/(128*16) endif ' tanktemp = 200 + (dt*(c6+100))/2048 'simpler form, less accurate?? tanktemp = 200 + dt2*(c6 + 100)/2048 offset = c2 + ((c4 - 250)*dt)/4096 + 10000 senstvty = c1/2 + ((c3 + 200)*dt)/8192 + 3000 tankpress = (senstvty*(d1 - offset))/4096 + 1000 BoundsCheck: if (tankpress > 8000) or (tankpress < 700) then debug 13, 10, "Bounds error. Tank = ",#tank, ", TankPress = ", _ #tankpress," mB", 13, 10 goto readtank 'retry until value is within bounds endif if tank = 0 then t0pressure = tankpress t0celsius = tanktemp ' debug "T0 D1, D2 = ", dec d1,", ", dec d2, ", T0 Pressure = ", dec t0pressure, ", Temp ", dec t0celsius, 13, 10 endif if tank = 1 then t1pressure = tankpress t1celsius = tanktemp ' debug "T1 D1, D2 = ", dec d1,", ", dec d2, ", T1 Pressure = ", dec t1pressure, ", Temp ", dec t1celsius, 13, 10 endif if tank = 2 then t2pressure = tankpress t2celsius = tanktemp ' debug "T2 D1, D2 = ", dec d1,", ", dec d2, ", T2 Pressure = ", dec t2pressure, ", Temp ", dec t2celsius, 13, 10 endif return

The minimum pauseus is 4 uS so there is now plenty of time for the data to stabilise before the clock strobe.

The Intersema pressure sensors are spectacular little temperature and pressure sensors and up until some recent changes have served me very well. With this new code, the conversion takes about 1 mS longer and the code is slightly bigger but I am now in control of the read & write process.

I hope someone finds this useful.

Cheers
BrianT

Hi Brian,

Glad you have it working. Can you tell a little more about what your doing with the pressure/temperature sensors? I do a lot of data acquisition work involving those types of measurements.

Thanks

Intersema pressure sensors

Hi Steve,
I use the MS5540 1 bar sansor for reading atmospheric pressure in a sample chamber where I must know the oxygen partial pressure very accurately. I also use this sensor for altitude in bird migration studies.

I use several MS5541 14 bar sensors in a gas mixer where I can mix O2, CO2 and N2 to 0.1 mB precision. I also use these in archival dataloggers which are surgically implanted in salmon, tuna, kingfish and penguins for physiological studies of aquaculture species.

Cheers
Brian

Re: SHIFTIN SHIFTOUT timing problem

Hi All!
I am very new to all of this and trying to learn and study what and how those of you who know this very well are doing. Is there any chance I could see the whole program/code for the MS5541 for a single unit? It would be very much appreciated.

Thanks, Ed

MS5441CM code example

Hi Ed,

Here is a code snip for driving the Intersema MS5541.

Code:

'************************* Defines ***************************** DEFINE OSC 4 'Define crystal frequency DEFINE DEBUG_REG PORTB 'Debug output pin port DEFINE DEBUG_BIT 6 'Debug output pin bit DEFINE DEBUG_BAUD 19200 'Debug baud rate DEFINE DEBUG_MODE 0 'Debug mode: 0 = True, 1 = Inverted '************** Intersema Variables ********************************* C1 var word ' 5540 Pressure sensitivity C2 var word ' 5540 Pressure Offset C3 var word ' 5540 Temp Coef of pressure sensitivity C4 var word ' 5540 Temp Coef of Pressure Offset C5 var word ' 5540 Reference temperature C6 var word ' 5540 temp coef of Temp reading ' C1 to C6 are in EEROM as VAL.byte0, VAL.byte1 from 108 to 159 D1 var word ' raw pressure word from Intersema sensor D2 var word ' raw temperature word D1Flag var bit W1 var word ' coefficient from 5540 W2 var word ' coefficient from 5540 W3 var word ' coefficient from 5540 W4 var word ' coefficient from 5540 ' W1 to W4 are NOT stored in EEROM - they are not needed again. dT var long ' intermediate calc value dT1 var long ' intermediate calc value dT2 var long UT1 var word ' Calibration temperature II var byte 'used ONLY within Intersema routines IJ var byte IK var byte IL var byte ILoop var word CalFlag var bit 'EEROM 99. Used to reduce wear on EEROM 'General purpose Intersema and DS1629 RTC/Temperature variables ClkChk var word '= 8192 if IntRC clock is exactly on frequency TimeFlag var bit TempRead var word CntRem var word CntPerC var word IW var long IX var long IY var long IZ var long T2 var long 'Second order Temperature correction P2 var long 'Second order Pressure correction Offset var long Senstvty var long Pressure var long ' Celsius var long 'a LONG allows negative temperatures goto endofsubroutines ' jump subroutines at startup '*************************** Subroutines ***************************** ResetIntersema: ' need 32768 @ 50% for Intersema on CCP2. TRISB = %10000001 : TRISD.7 = 0 'DIn, DOut & SClk high presspwr : pause 100 : hpwm 2, 127, 32767 : pause 50 shiftout din, sclk, 0, [85, 85, 0\5] ' Sense of Din is IN to 5541 pauseus 100 return FetchWord: shiftin dout, sclk, 2, [ij, ii, ik\1] 'IJ is hi byte, II is lo byte, IK is a dummy and discarded return CalSensor: read 99, calflag : if calflag = 1 then calsensordone debug 13, 10, "Fetch Intersema data", 13, 10 ' This fetches and unpacks the factory calibration coefficients ' from W1 ~ W4. W values need not be stored. ' These bitmaps are unpacked into the 6 working coefficients ' C1 to C6 which must be stored in EEROM for later use. 'W1 gosub resetintersema shiftout din, sclk, 0, [87, 1\5] ' Send W1 pattern to all sensors gosub fetchword ' get reply W1.byte0 = ii W1.byte1 = ij 'W2 gosub resetintersema shiftout din, sclk, 0, [215, 0\5] ' Send W2 pattern gosub fetchword W2.byte0 = ii W2.byte1 = ij 'W3 gosub resetintersema shiftout din, sclk, 0, [55, 1\5] ' Send W3 pattern gosub fetchword W3.byte0 = ii W3.byte1 = ij 'W4 gosub resetintersema shiftout din, sclk, 0, [183, 0\5] ' Send W4 pattern gosub fetchword W4.byte0 = ii W4.byte1 = ij 'Unpack W1 ~ W4 into C1 ~ C6 coefficients 'C1 C1 = W1 >> 3 write 108, c1.byte0 write 109, c1.byte1 'C2 C2 = ((W1 & %0000000000000111) << 10) + (W2 >> 6) write 110, c2.byte0 write 111, c2.byte1 'C3 C3 = W3 >> 6 write 112, c3.byte0 write 113, c3.byte1 'C4 C4 = W4 >> 7 write 114, c4.byte0 write 115, c4.byte1 'C5 C5 = ((W2 & %0000000000111111) << 6) + (W3 & %0000000000111111) write 116, c5.byte0 write 117, c5.byte1 'C6 C6 = W4 & %0000000001111111 write 118, c6.byte0 write 119, c6.byte1 ' high pgc : pause 1 ' debug "Intersema Factory data ", $0D, $0A, "W1 = ,"_ ' , #w1, ", W2 = ,", #w2, ", W3 = ,", #w3, ", W4 = ,", #w4, $0D, $0A ' debug "Derived coefficients", $0D, $0A, "C1 = ,", #C1, ", C2 = ,", #C2,_ ' ", C3 = ,", #C3, ", C4 = ,", #c4, ", C5 = ,", #C5, ", C6 = ,", #C6.byte0,_ ' $0D, $0A ' read 99, calflag : if calflag = 0 then write 99, 1 CalSensorDone: return ReadIntersema: ' ' D1 is Pressure - D2 is Temperature ' Uses LONG datatype to handle negative temperatures ' This routine reads the sensor and returns Pressure word ' and Celsius long ' A, II, IJ, W and X are all destroyed gosub resetintersema 'D1 shiftout din, sclk, 0, [47, 0\5] ' Select D1 pattern While dout = 1 : wend 'Convert5541Delay: gosub fetchword ' This returns ii = lobyte, ij = hibyte from the sensor D1.byte0 = ii D1.byte1 = ij 'D2 shiftout din, sclk, 0, [79, 0\5] ' Select D2 pattern While dout = 1 : wend gosub fetchword D2.byte0 = ii D2.byte1 = ij CalcTempPress: '32 bit signed arithmetic version. Handles negatives. read 108, c1.byte0 read 109, c1.byte1 read 110, c2.byte0 read 111, c2.byte1 read 112, c3.byte0 read 113, c3.byte1 read 114, c4.byte0 read 115, c4.byte1 read 116, c5.byte0 read 117, c5.byte1 read 118, c6.byte0 'formulae for DS5541 are NOT the same as for DS5540 ut1 = 8*c5 + 10000 dt = d2 - ut1 Celsius = 200 + dt*(c6 + 100)/2048 offset = c2 + ((c4 - 250)*dt)/4096 +10000 senstvty = c1/2 + ((c3 + 200)*dt)/8192 + 3000 pressure = (senstvty * (d1 - offset))/4096 + 1000 'NOT applying second order temperature correction in this 'version. 'Note 2nd order correction formula ambiguity in datasheet. if celsius < 0 then 'high bit of 32 bit number is set temp2 = 1000 - celsius else temp2 = 1000 + celsius d[17] = temp2.byte0 d[18] = temp2.byte1 endif if calflag = 0 then high pgc : pause 1 debug "MS5541 Celsius = ", sdec Celsius/10, ".", dec1 celsius//10, _ ", Pressure = ", dec pressure, " mBar, recorded as ",_ dec temp2, 13, 10 endif return EndOfSubRoutines: '*********************** Initialise ***************************** FetchDepth: gosub readintersema 'debug "T2 = ", dec temp2, 13, 10 debug dec (temp2 - 1000)/10, ".", dec1 (temp2 - 1000)//10, _ ", ", #pressure, " mBar", 13, 10 'this returns Pressure & Celsius, both words. hpwm 2, 0,0 'turn off Mclk ShutDown: gosub shutdownmemory gosub lowestpower end ZZZZZ:

HTH
Brian

Still Confused

My guess is that Brian is busy? I was wondering if anyone would know how to do the PIC pin assignments? Several things have me lost such as in the code there is only 1 reference to the sensor's MCLK pin? Mostly I am familiar with using:
' ** Declare Pins Used **
Sclk Var PortB.0
Din Var PortB.1
This code has me completely lost!

Thanks in advance, eventually it will all come back to me, Ed

Intersema issues

Hi Ed,
Yes you do need a set of hardware defines such as
MClk VAR PortC.1
SClk VAR PortC.4

MClk in my design is driven by CCP2 so it cannot be randomly assigned but any of the other Intersema pins can be attached to any PIC pins.

YOU, and only you, can write the hardware defines as they are dependent on how you have laid out your circuit board.

Or have I missed your question?

HTH
BrianT

Re: SHIFTIN SHIFTOUT timing problem

Thanks Brian! :)
Yes I noticed that depending upon the PIC there is only one pin marked as CCP2. My guess is that by using HPWM the PIC knows to use this pin and it still must have a hardware definition? MCLK is shown as a comment so it has been confusing to know what to do for the hardware defines. Another thing I did not understand is why use CCP2 and not CCP1?

For 3.3 v to 5.0 v conversion (bi-directional) a device that does this known as the ADG3304 if this is of value. The device can also be used for other voltage level changes.

Variations in atmospheric pressure causes the zero reference point (the surface of the water) to change so to maintain accuracy a simple water detector (two transistors) could be used to set the zero reference (surface) point.

Thanks for answering and hope I have made some small contribution to you and others.

Ed

A little help with understand the code in this post Please

A little help please.

high presspwr ' there is no pin defined as presspwr

temp2 = 1000 - celsius ' there is no variable named temp2

d[17] = temp2.byte0
d[18] = temp2.byte1 ' There is no array named d.

high pgc ' there is no pin defined as pgc

gosub shutdownmemory ' there is no sub-routine with this name

gosub lowestpower ' there is no sub-routine with this name either end '

I do not wish it to stop or end just continue to get int information.

Thanks, Ed

Re: SHIFTIN SHIFTOUT timing problem

Quote:

high presspwr ' there is no pin defined as presspwr

If that is so, then pick one and make it so, some thing like

Code:

presspwr var PortA.0

Quote:

temp2 = 1000 - celsius ' there is no variable named temp2

Code:

temp2 var word 'a byte only holds 0-255

Quote:

d[17] = temp2.byte0
d[18] = temp2.byte1 ' There is no array named d.

assigns value to 2 bytes in array, set up array,

Code:

d var byte[18]

Quote:

high pgc ' there is no pin defined as pgc

again make a pin do this by assigning it to that duty

Code:

pgc var PortA.1 ' or some other unused pin

Quote:

gosub shutdownmemory ' there is no sub-routine with this name

Make a sub directory or remove the call to it and send the code elsewhere using
goto or gosub as appropriate.

gosub lowestpower ' there is no sub-routine with this name either end '

Quote:

I do not wish it to stop or end just continue to get int information.

same answer as above. this is the disadvantage to using code you did not write, you are forced into the position of clairvoyant as you try to imaging what the programmer envisioned.
Probably the best argument for chewing through someone else's code is to learn from it, the cost is the frustration of trying to understand it.
I hope you found something useful in my rant,
JS