Clocking data - the best way to do it?

[Grogster]

I have to be able to clock 16-bit words into a SOMO sound module using the bit-banging approach. I know what the words are going to be.

Is there a more simple method then just:

start:
  pulsout 1,200  'Start bit
  high 2  'Put data on data line
  pulsout 1,50  'Clock the module
  high 2  'Put data on data line
  pulsout 1,50  'Clock the module
  low 2  'Put data on data line
  pulsout 1,50  'Clock the module
  .
  .
  .

This is long and memory intensive(although it does work), especially if you need to store several different commands - 34 lines per command(16x 2 lines for every bit + 1x start bit and 1x stop bit) - there must be a more efficent method. Can anyone offer me any alternatives?

[westaust55]

Have a look at the code in PICAXE manual 2 under the SHIFTOUT command.

Starts at page 192 and there are bit-bashing examples on page 193.

You could use a word instead of a byte and change the bits value from 8 to 16

[Grogster]

OK, thanks, but still a little confused - where do I load the word I want to send?
I think this must be w6 in the symbols list at the start of shiftin, so do I just plop in the decimal value of the binary word I want to send at that point?

Example:
Say I want to send 65000, do I have a line which says let w6 = 65000(or let var_out = 65000), then gosub the routine?

Assume that symbol bits = 16 and symbol MSBvalue = 65535.

EDIT: Not working - all I get is sdata high all the time with the sclk pulsing away in the background, but there are no lows as their should be. 65000 = 1111110111101000 binary, so there should be some pulses where the data-LED is off. I have two LED's on the two pins - one on the sclk pin, and one on the sdata pin so I can see what is happening, but at no point in the proceedure does the sclk LED pulse while the sdata LED is off, because the sdata LED remains on from fire up until power-down. *sigh* I increased the pulsout time to 5000 to slow things down so I can see what is going on, and so it is not so fast I can't visually follow it.

Enough for tonight - 10 to one in the morning here - need sleep...

[westaust55]

OK, thanks, but still a little confused - where do I load the word I want to send?
I think this must be w6 in the symbols list at the start of shiftin, so do I just plop in the decimal value of the binary word I want to send at that point?

Example:
Say I want to send FFFFh, do I have a line which says let w6 = 65535(or let var_out = 65535), then gosub the routine?

Assume that symbol bits = 16 and symbol MSBvalue = 65535.

Yes you are on the right path/track.

SYMBOL var_out = w6
SYMBOL bits = 16
SYMBOL MSBValue = $8000
var_out = 65535

gosub shiftout_MSBFirst


‘ ***** Shiftout MSB first *****
shiftout_MSBFirst:
for counter = 1 to bits ‘ number of bits
mask = var_out & MSBValue ‘ mask MSB
low sdata ‘ data low
if mask = 0 then skipMSB
high sdata ‘ data high
skipMSB: pulsout sclk,1 ‘ pulse clock for 10us
var_out = var_out * 2 ‘ shift variable left for MSB
next counter
return

[Grogster]

Cheers - will try that shortly and let you know.
I changed the var_out from 65535 to 65000 so there were some low's in the binary word, otherwise the LED would not change if var_out was all 1's.
Doing conversion of 8000h is 1000000000000000, which puts the MSB at bit-16, so this is where I was stuffing up last morning
It was very late...
Sleep has recharged my brain a little, but I still need coffee.

EDIT1: Not working. I get ONE pulse one the sclk, then sdata stays high and there are no more pulses from sclk. More coffee...

EDIT2: Put a wait 1 before the next x in the gosub, and I can see what is happening now, but the data is inverted - what should be highs are lows and vise-versa. I checked this bit-by-bit, and it is definetly inverted. Sending 65000 decimal, which is 1111110111101000 binary, and the data line shows me 0000001000010111 - 535 decimal. Confused.

EDIT3: Swapped high sdata for low sdata and vise-versa in the gosub, and the data is almost correct now, but the last 2-bits pulse through as highs(can just visually detect a flash from the sdata LED during the clock pulse) when they should be low. The actual output binary is therefore 1111110111101011 which is 65003 so still not right. The experiment continues...

[Grogster]

I've re-written a routine to do what I want, using DATA/EEPROM statements and the READ command.

output 1	'Output 1 is the clock line
output 2	'Output 2 is the data line
low 1
low 2

symbol x = b1
symbol bit = b2


stp:
  pulsout 1,2500		'Start bit pulse
  for x = 1 to 16
    read x,bit
    bit = bit - 48
      if bit=1 then high 2
        endif
      if bit=0 then low 2
        endif
  pulsout 1,1000		'Clock the module
  pause 500
  debug bit
  next x
  wait 5
  goto stp
  
data_sub:
data 1,("1111110111101000")	'Command 65000 binary

This works extremely well, and also allows me to keep the binary "Word" within the data statements. This method also does not have the problem of the last 2-bits being high when they should not be. Plus this is easier for me to follow then the other method.

This needs a bit more tidying up, but it works beautifully.

If I need more then 15 commands, I will have to use external EEPROM chip, but it might be a good chance for me to play with one of those at the same time...

[kewakl]

If I need more then 15 commands, I will have to use external EEPROM chip, but it might be a good chance for me to play with one of those at the same time...

Could you use TABLE/READTABLE to store some data in PROGRAM MEMORY?

[Grogster]

Could you use TABLE/READTABLE to store some data in PROGRAM MEMORY?

A beautiful idea.
I'd have to change chips from 18X to 20X2, but it would give me a chance to play with the 20X2, and it is a few bucks cheaper too.

[westaust55]

here is a version - added a few more SYMBOL statements to clarify
which does work using the method in manual 2

SYMBOL var_out = w6
SYMBOL counter = b3
SYMBOL MASK = w5
SYMBOL bits = 16
SYMBOL MSBValue = $8000
SYMBOL sdata = 2
SYMBOL sclk = 3

var_out = $5555

gosub shiftout_MSBFirst


‘ ***** Shiftout MSB first *****
shiftout_MSBFirst:
for counter = 1 to bits ‘ number of bits
mask = var_out & MSBValue ‘ mask MSB
low sdata ‘ data low
if mask = 0 then skipMSB
high sdata ‘ data high
skipMSB: pulsout sclk,1 ‘ pulse clock for 10us
var_out = var_out * 2 ‘ shift variable left for MSB
next counter
return

to use the table memory as suggested by kewakl, this is also available in the X1 PICAXE parts.

[hippy]

A note on optimising code ...

if bit=1 then high 2
endif
if bit=0 then low 2
endif

This can be represented as -

If bit = 1 Then
High 2
Else
Low 2
End If

Or -

Low 2
If bit = 1 Then
High 2
End If

And best of all -

outpin2 = bit