I though I'd post the little piece of code i write for bit-bang interfacing of this DAC chip with picaxe 18x.
In the manual and in the code examples folder, that comes with the PE, there seems to be a small error in the provided shiftout routines. I'm referring to this part:
The low and high statements seem to have been reversed, in the way it's printed in the manual and in the sample it makes no sense, and i had to swap them to make it work.
Anyways, here is the small test program i came up with, i hope anyone getting started with this IC might find it useful. All it really does is increasing the dummy variable, and then sending it via SPI to the IC, running in continous loop.
In the manual and in the code examples folder, that comes with the PE, there seems to be a small error in the provided shiftout routines. I'm referring to this part:
Code:
shiftout_MSBFirst:
for counter = 1 to bits ' number of bits
mask = var_out & MSBValue ' mask MSB
[COLOR="Red"]low sdata[/COLOR] ' data low
if mask = MSBValue then skipMSB
[COLOR="Red"]high sdata[/COLOR] ' data high
skipMSB:
pulsout sclk,1 ' pulse clock for 10us
var_out = var_out * 2 ' shift variable left for MSB
next counter
returnAnyways, here is the small test program i came up with, i hope anyone getting started with this IC might find it useful. All it really does is increasing the dummy variable, and then sending it via SPI to the IC, running in continous loop.
Code:
#rem
18.2.2010
An example code how to bit-bang interface to the MCP4921 / 4922 12-bit DAC IC, with picaxe 18x.
"value" is the value transmitted to dac output, and in this test it is increased by 2 on each program run cycle.
ldac pin is tied down, so the outputs are latched immediately in this test after completing the SPI transfer.
indicator led is connected to output 0
#endrem
#picaxe 18x
#no_data
'#no_table
'----------------------------------------------
'SYMBOLS
symbol sclk = 1 ' clock (output pin)
symbol sdata = 2 ' data (output pin for shiftout)
symbol led = 0 ' mandatory indicator led
symbol cs = 3 ' chip select
symbol counter = b1 ' variable used during loop
symbol mask = w2 ' bit masking variable
symbol var_out = w1 ' data variable used during shiftout
symbol value = w3 ' test value to be transmitted to the DAC
symbol bits = 16 ' number of bits
symbol MSBvalue = 32768 ' MSBvalue (=128 for 8 bits, 512 for 10 bits, 2048 for 12 bits)
'----------------------------------------------
init:
high cs 'put the chip select to idle
pause 100
setfreq m8
do
if value > 4095 then
value = 0
endif
toggle led
'bit 15; 1= write to DACb 0= write to DACa
'bit 14; 1= enable input buffer 0 = input buffer is disabled
'bit 13; 1= outputgain at 1x 0 = 2x output gain
'bit 12; 1= outputs enabled 0 = outputs are floating (high impedance)
'bits 11-0 Transferred data, MSb first.
var_out = value | %0011000000000000 'mask the 4 control bits --> writing to DACa, input buffer disabled, output at 1x gain, outputs enabled.
var_out = var_out & %0011111111111111
'sertxd (#var_out)
'*****spi transfer
low cs 'low chip select
gosub shiftout_MSBFirst
high cs 'cs back to idle, latches data to output
value = value + 2 'increase dummy variable
loop
' ========================================================================
' ***** Shiftout MSB first *****
' Shift out the data MSB first from variable var_out
' Using clock output pin sclk
' Using data output pin sdata
' Note the number 128 (used twice) is the mask byte for MSB of 8 bits
' If using 10 bits use 512, 12 bits use 2048 etc
shiftout_MSBFirst:
for counter = 1 to bits ' number of bits
mask = var_out & MSBValue ' mask MSB
high sdata ' data high WARNING - IF YOU COPY THIS PART FROM THE EXAMPLE's folder CODE, REMEMBER THAT.
' THE HIGH AND LOW STATEMENTS HERE ARE REVERSED.
if mask = MSBValue then skipMSB
low sdata ' data low
skipMSB:
pulsout sclk,1 ' pulse clock for 10us
var_out = var_out * 2 ' shift variable left for MSB
next counter
return
' ========================================================================
Last edited:
. . . so little time