Serial randomness!

[london alex]

Hi everyone,

Hoping you might be able to help me with a little project I’ve been working on….

I’ve been trying to create a code that reads in a value (b0) from an
a/d converter, this then goes to a timer routine which loops ‘b0’ amount of times and then sends PORTB.3 high. I’ve programmed the following onto a pic16f628a and then added it to the circuit…. from first impressions it all looks great! However…. By watching the LED’s attached to pins 5,6,7 and 8 I can see that it’s adding up a different amount each time, even though the value from the A/D converter should be the same. Can anyone spot where I’m going wrong here as it’s left me pretty confused!

Many thanks, Alex

-----------------------------------------------

CMCON = 7
INCLUDE "modedefs.bas"
TRISB = 1
TRISA.0 = 1
ti var byte 'Initial time delay
b0 var byte 'serial value from a/d converter
timer var byte
ti = 1000 'timer value
timer = 0
b0 = 0


start:

portb = 128 'flash
pause 400
portb = 0
pause 400
IF porta.0 = 1 THEN start


Serial_in:

low 1 'bring I/O clock low
low 2
pause 1000
b0.7 = PORTB.0
pulsout 1,1
pause 500
b0.6 = PORTB.0
pulsout 1,1
pause 500
b0.5 = PORTB.0
pulsout 1,1
pause 500
B0.4 = PORTB.0
pulsout 1,1
pause 500
b0.3 = PORTB.0
pulsout 1,1
pause 500
b0.2 = PORTB.0
pulsout 1,1
pause 500
b0.1 = PORTB.0
pulsout 1,1
pause 500
b0.0 = PORTB.0
pulsout 1,1
pause 500
high 2
pause 1000



Timer_routine:

b0 = b0 * 5
if timer > b0 then Execute 'check
portb = 16
pause ti
timer = timer + 1
portb = 32
pause ti
timer = timer + 1
portb = 64
pause ti
timer = timer + 1
portb = 128
pause ti
timer = timer + 1
goto Timer_routine


Execute:

timer = 0
portb = 8 'send signal to relay
pause 4000
b0 = 0 'reset b0
goto start

[skimask]

Hi everyone,
Hoping you might be able to help me with a little project I’ve been working on….
I’ve been trying to create a code that reads in a value (b0) from an
a/d converter, this then goes to a timer routine which loops ‘b0’ amount of times and then sends PORTB.3 high. I’ve programmed the following onto a pic16f628a and then added it to the circuit…. from first impressions it all looks great! However…. By watching the LED’s attached to pins 5,6,7 and 8 I can see that it’s adding up a different amount each time, even though the value from the A/D converter should be the same. Can anyone spot where I’m going wrong here as it’s left me pretty confused!
Many thanks, Alex


Where's the ADC code?
The output from the ADC should be the same...key word is 'should'.
Is your ADC input varying at all?
Are you sampling it slow enough as the datasheet suggests?
Are your parameters for the ADC (sample time, etc.) correct?
What is the input impedance to your ADC pin?
For all I know, there's a nuclear fission reactor power generating station connected to AN0 on the PIC, or it could be a small butterfly. I don't know.

[mister_e]

seems to be an external ADC on PORTB.0. Setting sampling time, clock source etc... on a 16F628 :eek: that will be hard ;)

However i don't think it's working like that. If we knew the ADC model, we could elaborate a bit much. Almost sure it's an SPI type... SHIFTIN/SHIFTOUT would help.. but.. i only guess :D

[london alex]

Yeah sorry guys, should have been a bit clearer! I'm using an external TLC549CP A/D converter which has:

ADC 'data out' pin attached to pin 0 on the pic.
ADC i/o clock pin attached to pin 1 on the pic and..
ADC CS(active) pin attached to pin 2...

Attached to the ADC is a potentiometer which is supplying the variable voltage (0-5V). Throughout my testing I haven't been adjusting it and so the serial output should remain the same if it was working correctly.

Haven't tried SHIFTIN/SHIFTOUT but will have a look into it... cheers!!

[Darrel Taylor]

Alex,

When you do something like PORTB = 8, it sets all the pins in PORTB.

Since PORTB.2 is the A/D's Chip Select pin, every time you turn on an LED or Relay, you are also Enabling the A/D converter. Probably getting it confused.

And that chip can be clocked at up to 1 Mhz.
6 seconds is an awful long time to read 8 bits.
<br>

[london alex]

Hey Darrel,

Thank you loads for your response! I'm currently away from home and so unable to test your theory, but i'm convinced that will be the cause of the issue! I'll keep you updated as to when I can test it and thanks to everyone who helped.

Cheers,
Alex