SHIFTIN SHIFTOUT timing problem

[BrianT]

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.

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

[Steve_88]

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

[BrianT]

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

[Ramius]

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

[BrianT]

Hi Ed,

Here is a code snip for driving the Intersema MS5541.

  
'************************* 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

[Ramius]

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

[BrianT]

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