In SX Microcontrollers, SX/B Compiler and SX-Key Tool, alex41 wrote:

[2]Hello again,[/2]

[2][/2] 

[2]I have written the following program to use the LTC1257 12bit DAC. I gathered all the info I could and wrote the code. The N&V column #4 and #43 were very helpful. Of course I read the LTC1257 datasheet too. It seems these articles were written before the SHIFTIN and SHIFTOUT commands were available, so I'm kinda shooting in the dark with setting those up.[/2]

[2][/2] 

[2]The program is basically working, but not 100%.[/2]

[2][/2] 

[2]I'm using a pot with RCTIME to input a number between 0 and 4095. The code seems to be working somewhat, but the output is from 0v to about 3.6 volts. I'm looking for a range of 0 to 5v. The output of the LTC1257 goes through a LM356 op amp and I've read the voltage out of the chip and the op-amp and they are the same, so it appears to be hooked up correctly.[/2]

[2][/2] 

[2]I would guess the code with the SHIFTIN may not be correct, but really don't know where to go from here. Any input?[/2]

[2][/2] 

[2]Thanks,[/2]

[2]Alex[/2]

 

Code is below

 

 

 

 

 

' =========================================================
'
'   File...... LTC1257R1.SXB
'   Purpose... Simple program to use LTC1257 DAC
'   Author.... Alex41 
'   E-mail....  
'   Started... Feb 18 2008
'   Updated... Feb 19 2008
'
' =========================================================

' Revision 1,

'

' -------------------------------------------------------------------------
' Program Description
' -------------------------------------------------------------------------
'
' This is a simple program to test programming of the LTC1298 DAC chip
' A pot is used to provide a value for the DAC to use
'
' Chip connections,
'
' 1  CLK - RC.0  8  Vcc to 9v pos 
' 2  Din - RC.1  7  Vout - output amplified by LM358
' 3  LOAD- RC.2  6  Vref - 5v pos
' 4  Dout - not used 5  Gnd  - Ground
'
' Note - pin 8 on chip is provided with 9v to allow a 0-5v output range

' -------------------------------------------------------------------------
' Device Settings
' -------------------------------------------------------------------------

DEVICE          SX28, OSCXT2, TURBO, STACKX, OPTIONX, BOR42
FREQ            4_000_000
ID              "LTC1257"

' -------------------------------------------------------------------------
' IO Pins
' -------------------------------------------------------------------------


Clk  PIN RC.0 OUTPUT
Din  PIN RC.1 OUTPUT
PinLoad  PIN RC.2 OUTPUT

Potpin  PIN RC.7 OUTPUT

 

' -------------------------------------------------------------------------
' Constants
' -------------------------------------------------------------------------

 

' -------------------------------------------------------------------------
' Variables
' -------------------------------------------------------------------------


TmpW1  VAR Word
Pottime  VAR Word

 

' =========================================================
  PROGRAM Start
' =========================================================

  

' -------------------------------------------------------------------------
' Subroutine Declarations
' -------------------------------------------------------------------------

DELAY_MS SUB 1, 2

' -------------------------------------------------------------------------
' Program Code
' -------------------------------------------------------------------------

Start:
  ' initialization code here

Main:      ' main code here

DO  
  ' RCtime - read pot to get value
  HIGH potpin   ' charge the capacitor
  PAUSEUS 300   ' Pause for 50 us
  RCTIME Potpin, 1, Pottime ' measure in 2 us units
  IF Pottime > 4095 THEN ' max input of 4095 for DAC chip
    Pottime = 4095
  ENDIF
  PinLoad = 0                 ' activate chip to receive data
  SHIFTOUT Din,Clk,MSBFIRST,Pottime_MSB ' send high nib
  SHIFTOUT Din,Clk,MSBFIRST,Pottime_LSB ' send low byte
  PinLoad = 1              ' de-active chip to output voltage
  DELAY_MS 500
LOOP

 

' -------------------------------------------------------------------------
' Subroutine / Function Code
' -------------------------------------------------------------------------

' Use: DELAY_MS duration

SUB DELAY_MS
  IF __PARAMCNT = 1 THEN
    tmpW1 = __PARAM1                            ' save byte value
  ELSE
    tmpW1 = __WPARAM12                          ' save word value
  ENDIF
  PAUSE tmpW1 
  ENDSUB


' =========================================================
' User Data
' =========================================================

---------- End of Message ----------


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