Serout/serin issues, advice required

[Agent36]

Hi,
I have been trying to send data between two pics, my end goal is to use a wireless link. At the moment this link is hardwired. The code below is supposed to read a adc input, then encode it using manchester encoding and send it to a receiving pic. Code below;

@ DEVICE PIC12F683, INTRC_OSC_NOCLKOUT
' System Clock Options (Internal) 
@ DEVICE PIC12F683, WDT_ON
' Watchdog Timer
@ DEVICE PIC12F683, PWRT_ON
' Power-On Timer
@ DEVICE PIC12F683, MCLR_OFF
' Master Clear Options (Internal)
@ DEVICE PIC12F683, BOD_OFF
' Brown-Out Detect
@ DEVICE PIC12F683, CPD_ON
' Data Memory Code Protect
@ DEVICE PIC12F683, PROTECT_ON

OSCCON  = %01110000     ' Internal 8MHz osc
'PICBASIC PROGRAM
ANSEL = %00010000
ADCON0 = %10000001
VRCON = 0
CMCON0 = 7
DEFINE ADC_BITS 10      'Defines bit resoloution
DEFINE ADC_CLOCK 3		'Defines adc clock speed	
DEFINE ADC_SAMPLEUS 50	'Defines sammple time of 50mS
'DEFINE OSCCAL_1K 1
Define OSC 8                ' Define oscilator speed
INCLUDE "modedefs.bas"

txout VAR GPIO.0 : Output txout : dataout VAR BYTE
ledcount VAR BYTE
speed var byte
Manch var byte
index var byte
led1 VAR GPIO.1 : Output led1
key VAR GPIO.5 : Input key 
gpio = %00000000
led1 = 1 : pause 500 : led1 = 0 
trisio.4=1
trisio.2=0

mainloop:
ansel = %00001000		'Turns on a2d two
ADCIN 3,speed
speed = speed/4
hpwm 2,speed,7000
IF key = 0 Then 'button not pressed
GoTo mainloop
EndIF
IF key = 1 Then
Pause 50 'wait 50ms for switch to debounce then check again
IF key = 1 Then 'Tx data out
call encode
dataout = $55 '($55 = manchester encoded $0)
SerOut txout, n2400, [ dataout, dataout, dataout, dataout, dataout ]
pause 10
SerOut txout, n2400, [ $aa,Manch ]
EndIF
EndIF
goto mainloop

Encode:
   For Index = 0 to 7		' loop 8-bits
     Manch.0[(Index<<1)] = ~speed.0[Index] ' Encode bits 0,2,4,6,8,10,12,14 in Manch
     Manch.0[(Index<<1)+1] = speed.0[Index]' Encode bits 1,3,5,7,9,11,13,15 in Manch
   Next Index
   Return

End

Once sent the following is supposed to receive it and decode it. The encode/decode routines for the tx'd info was an example posted on this forum.
Receiver code;

@ DEVICE PIC12F683, INTRC_OSC_NOCLKOUT
' System Clock Options (Internal) 
@ DEVICE PIC12F683, WDT_ON
' Watchdog Timer
@ DEVICE PIC12F683, PWRT_ON
' Power-On Timer
@ DEVICE PIC12F683, MCLR_OFF
' Master Clear Options (Internal)
@ DEVICE PIC12F683, BOD_OFF
' Brown-Out Detect
@ DEVICE PIC12F683, CPD_ON
' Data Memory Code Protect
@ DEVICE PIC12F683, PROTECT_ON

OSCCON  = %01110000     ' Internal 8MHz osc
ANSEL = %00000000
CMCON0 = 7
Define OSC 8                ' Define oscilator speed
INCLUDE "modedefs.bas"
rxin VAR GPIO.5 : Input rxin : datain VAR BYTE
Manch var word
index var byte
datain = 0
trisio.2 = 0
mainloop:

SerIn rxin, n2400, [$aa], Manch
call decode
hpwm 2,datain,7000
goto mainloop

Decode:
   For Index = 0 to 7   ' loop for 8 bits
     datain.0[Index] = ~Manch.0[Index<<1]' ByteOut=NOT Manch bits 0,2,4,6,8,10,12,14
   Next Index  
   Return

End

I can send a single byte of data between two pics, any byte that gives an even spead of 1's and 0's etc for the manchester encoding works fine. If anyone can see where I have gone wrong can they let me know please. Most of the time I fine my answers on this forum, but not this time.
thanks for your time Nick

[skimask]

2 PICs, both running on the internal clock, TX'ing and RX'ing 2400 baud serial...
Almost sounds like a recipe for 'no worky' to me.
Any way you can modify the circuit to plug in a crystal or resonator and try it out that way?

[Agent36]

Hi Skimask,
I had the simple data tx/rx working ok over wireless on the internal clock, I could try it on crystals (once I order some). Does the code look ok apart from that? Have not used serin/out much.
regards Nick

[skimask]

I'll take a better look at the code later on...(heading out the door)...
I think the fact that it was working and now it's not working is just luck. Internal freq varies with temp, voltage, humidity, sun spot cycle, color of pants, you name it, it varies because of it...ok maybe not everything
Moral of the story, usually internal osc's are hit/miss when using serial.

[Bruce]

SerOut txout, n2400, [ $aa,Manch ] is only sending $aa followed by the low byte of Manch.

SerOut txout, n2400, [ $aa,Manch.LowByte,Manch.HighByte] will send both bytes of Manch.

Modify the receive routine also. SerIn rxin, n2400, [$aa], Manch.LowByte,Manch.HighByte.

[Agent36]

Hi Bruce,
Thanks for that, was not 100% sure if I could send a word out in a single statement, just looked at the serout command in the manual and found the answer on the 2nd line.
I will modify the code later tonight and see what happens.
regards Nick

If anyone uses the code I have posted you need to change-- Manch var byte--to--Manch var word---in the Tx code. This have me stumped for 10 mins..lol.

[Agent36]

Hi Skimask and Bruce,
Thanks for the info, I now have my project up and running. The only other changes I had to make apart from the ones already listed, was to change the variables used in the ADC result and PWM output.
regards Nick

[BrianT]

If your system loses or gains half a bit time due to noise, clock slip, whatever, then Manchester goes out of sync and stays out for the rest of the message. BiPhase on the other hand is brought back into sync with the arrival of the very next '1' bit. BiPhase does not propagate errors. The code for biphase is virtually identical to manchester. Manchester needs very high accuracy clocks at both ends. BiPhase is much more tolerant of clock differences. The downside of biphase is that the channel needs a somewhat wider bandwidth.

Search for biphase code in the forum. I have posted on it before.

HTH
BrianT

[Agent36]

Hi Brian,
Thanks for the info, I have just searched biphase and found a couple of posts. How do you encode and decode in laymans terms?
This is as far as I have got with my rf;
I can toggle the output of a pic by sending a set of 0's and 1's to balance the data slicer, followed by a data byte. The rf modules I am using are AM and are supplied from RF solutions.
My next step was the code posted above, the aim of this was to control the speed of a motor using the rf modules and pics. By encoding the adc result and out putting it in the form of pwm.
Once I had the code working on the breadboard I transfered it to the Tx/Rx, at this moment in time I can control the motor at a 4 meter range, I have not tried any further as I have not had the time. This has all been acheived using the internal clock set at 8meg, I have taken skimasks advice and ordered some crystals to improve the timing errors. Any other improvements I can make would be an advantage.
Kind regards Nick

[mister_e]

You're code show a Manchester Encoding/Decoding routine... so it has to work. Maybe not a bad idea to have a bigger $AA preamble before sending your data.

Crystal are always welcome....

You could still waste quite of your time and try to fine tune the internal one with OSCTUNE register.