Help with ADC0838

GaryT

Has anybody used the the "ADC0838 to debug" object from the object library? I modified it a bit to work on the Demo board and send output to TV. But I don't understand how to use the SE pin, the Object doesn't seem to use it, but I can't get it to work either.
Any help is greatly appreciated.
Thanks,
Gary

Ale

That pin only controls whether the LSB (SE=0) or MSB (SE=1) come out first. It will work anyways. Did you check the clock line to see if it toggles ? CLK should be provided at all times and CS asserted when a conversion is started. I assume you checked the connectons between the prop and the ADC.

GaryT

Thanks Ale! I'm back on it this afternoon. Thanks for the info on the SE pin, I wasn't sure how to figure that out from the data sheet. I think that might be related to my problem. It appears that somewhere in the MUX addressing I'm setting some of the ports to single ended mode and some to differential mode. I think the problem is with the way I'm shifting the 4 mode bits + 1 start bit in on the DI pin. I'm setting up some output now to watch the CMD variable and see what's happening. I'm guessing that LSB or MSB mode would have quite an effect but I'll just leave it a no-connect for now.

Thanks again,
Gary

GaryT

I'm pretty sure it's the MUX addressing but I can't figure out why. I get good data for Channel 7, the MUX address is the same LSB and MSB. I've tried to shift in the other channel addresses both directions and get results that seem to indicate that I'm not doing it right. Maybe some dinner will help.

Thanks for any ideas,
Gary



'********************************
'* ADC 0838 Channel TVOut *
'********************************

'code compiled and revised by Bryan Kobe June, 2007
'revised for demo Board Gary T. Nov, 2008.
'This code is used for addressing and accessing all 8 channels on the ADC 0838
'It will address and TVOut all 8 channels, returning the value 0-255.

{{
ADC0838

│ Vcc(+5V)
┌───────────────┐ │
───┤1 ch0 VCC 20 ├───┤
─┤2 ch1 V+ 19 ├─ nc
─┤3 ch2 CS 18 ├──── pin3
─┤4 ch3 DI 17 ├──── pin2
─│5 ch4 CLK 16 ├─── pin1
─│6 ch5 SARS15 ├── pin4
─│7 ch6 DO 14 ├── pin0
─│8 ch7 SE 13 ├─ nc
┌─┤9 com VREf12 ├────── +5vdc
├─┤10 dgnd agnd11 ├─┐
│ └───────────────┘ │
└───────────────────┫
gnd

}}


CON

_clkmode = xtal1 + pll16x
_xinfreq = 5_000_000


{{ AD0 = %11000
AD1 = %11100 ' Note: See Datasheet MUX Addressing for more details
AD2 = %11001 ' Bit 4 = Start Bit, Bit 3 = SGL/DIF, Bit 2 = ODD/SIGN, Bit 1 = SELECT 1, Bit 0 = SELECT 0
AD3 = %11101
AD4 = %11010
AD5 = %11110
AD6 = %11011
AD7 = %11111}}

'AD0 = %11000
AD0 = %00011
AD1 = %00111
AD2 = %10011
AD3 = %10111 ' Note: See Datasheet MUX Addressing for more details
AD4 = %01011 'Bit 5 = 1, Bit 4 = Start Bit, Bit 3 = SGL/DIF, Bit 2 = ODD/SIGN, Bit 1 = SELECT 1, Bit 0 = SELECT 0
AD5 = %01111
AD6 = %11011
AD7 = %11111


' pin configuration

clk = 1
cs = 3
dataout = 0
datain = 2
sars = 4

OBJ

TVOut : "TV_Terminal"
num : "Numbers"

VAR

byte ADC ' Analog to Digital Channel Din Value. Set using CON values.
long datar ' 8 Bit return value from conversion
Word Addr

PUB main

dira[noparse][[/noparse]cs]~~ 'set Chip Select to output
outa[noparse][[/noparse]cs] := 1 'set Chip Select High
waitcnt(50_000_000 + cnt)
dira[noparse][[/noparse]clk]~~ 'set clk pin to output
outa[noparse][[/noparse]clk]:=1 'set clock pin low
waitcnt(50_000_000 + cnt)
dira[noparse][[/noparse]dataout]~ 'set data in pin to an input
dira[noparse][[/noparse]datain]~~ 'set data out pin to an output

'start the tv terminal
TVOut.start(12)
TVOut.out(2)

repeat

'GetADC(0)', Num#dec)
TVOut.str(string("Ch0="))
TVOut.str(num.ToStr(GetADC(0), Num#dec))
tvout.out(13)
'waitcnt(50_000000 + cnt)
TVOut.str(string("Ch1="))
TVOut.str(num.ToStr(GetADC(1), Num#dec))
tvout.out(13)
TVOut.str(string("Ch2="))
TVOut.str(num.ToStr(GetADC(2), Num#dec))
tvout.out(13)
TVOut.str(string("Ch3="))
TVOut.str(num.ToStr(GetADC(3), Num#dec))
tvout.out(13)
TVOut.str(string("Ch4="))
TVOut.str(num.ToStr(GetADC(4), Num#dec))
tvout.out(13)
TVOut.str(string("Ch5="))
TVOut.str(num.ToStr(GetADC(5), Num#dec))
tvout.out(13)
TVOut.str(string("Ch6 ="))
TVOut.str(num.ToStr(GetADC(6), Num#dec))
tvout.out(13)
TVOut.str(string("Ch7="))
TVOut.str(num.ToStr(GetADC(7), Num#dec))
tvout.out(13)

waitcnt(5_000_0000 + cnt)


PRI GetADC( chan ) : value

if (chan == 0)
ADC := AD0
if (chan == 1)
ADC := AD1
if (chan == 2)
ADC := AD2
if (chan == 3)
ADC := AD3
if (chan == 4)
ADC := AD4
if (chan == 5)
ADC := AD5
if (chan == 6)
ADC := AD6
if (chan == 7)
ADC := AD7

datar := write(ADC) 'write MUX Address to start conversion for ADC channel and set result to the datar value
return datar


PRI write( cmd ) : datar_val | i

outa[noparse][[/noparse]cs] := 0 ' set Chip Select Low
writeByte( cmd ) ' Write the command to start conversion for X port

repeat while (ina[noparse][[/noparse]sars] == 1) ' SARS goes LOW when sending LSB First Dout on ADC0838 (See Datasheet)
outa[noparse][[/noparse]clk] := 1 ' toggle sclk pin High (add delay here if clock is too fast) (clue: check duty cycle)
waitcnt(5000 + cnt)
outa[noparse][[/noparse]clk] := 0 ' toggle sclk pin Low
waitcnt(5000 + cnt)


' Ok now get the Conversion for this channel
repeat i from 0 to 7 ' read 8 bits
if ina[noparse][[/noparse]dataout] == 1
datar |= |< i ' set bit i HIGH
else
datar &= !|< i ' set bit i LOW
outa[noparse][[/noparse]clk] := 1 ' toggle sclk pin High
waitcnt(50_00 + cnt)
outa[noparse][[/noparse]clk] := 0 ' toggle sclk pin Low

outa[noparse][[/noparse]cs] := 1 ' set Chip Select High
return datar

PRI writeByte( cmd ) | i


repeat i from 0 to 3 ' ADC0838 has 1 start bit and 4 data bits
outa[noparse][[/noparse]datain] := cmd ' send LSB bit
'tvout.bin(cmd,6)
'tvout.out(13)
cmd >>= 1 ' shift to next bit
outa[noparse][[/noparse]clk] := 1 ' toggle sclk pin High (add delay here if clock is too fast) (clue: check duty cycle)
waitcnt(50_00 + cnt)
outa[noparse][[/noparse]clk] := 0 ' toggle sclk pin Low
waitcnt(50_00 + cnt)

Ale

What I see is that datain is P2, so in writeByte you are shifting starting bit 0, so you are losing 2 bits, unless the spin shifts for you the bit 0 to the bit indicated by datain... I do not know. It should be dataout !

On the other hand, a AD0838 needs 5 bits of command and you are only shifting 4... (repeat from 0 to 3). I imagine indention is ok also (use the code tags).

GaryT

Thanks for the ideas Ale, I think I have the dataout part to the ADC0838 going ok with this file. After a couple frustrating days, I think the returning data makes sense, as far as which channel it's reading.
Now I seem to have a strange problem with the results, they are half of what I expect. A 5v input on a pin returns 127, not 255. I think the pins are wired right, +V and Vref are at +5, Agnd is 0. I've tried 3 different ways to receive the data(shown in attached file) and get the same result either way, not the worst problem in the world to have, but I think I'm close to getting it right, and maybe suitable for the Object Library.

Any help greatly appreciated!
Thanks,
Garyt

Ale

You may be reading the bits off-time.

CannibalRobotics

I've got some ADC0838 code working back at the shop. I've been down this road before. (If you want it let me know.)
Anyway, look very closely at the timing diagram for this chip. The setup word and data bit shift timing are different. The last clock pulse of the setup is the first pulse of the data transmission. It's also wierd in that the symetrical data output shares the LSB in the middle AND THAT CLOCK CYCLE. The diagram shows an extra 3 clocks at the very wend of the cycle, I found that these seem to be necessary before the next sample.
(Look at page 11 of the attachment.)
Jim-

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