SMPTE Timecode reader

[docwisdom]

Brian,
Thanks for the great help thus far. Here is where I am at the moment.
Camera timecode out is wired to portc.2 and shield is connected to the circuits ground.
So far, I get the 'TC reader' greeting on the LCD but no readout of Timecode.
I threw in some LCDOUT lines for diagnostics. It gets to Found 0 and repeats there. So Found 1 doesn't seem to be occurring. Unless my pauses are causing problems.

One thing that stand out in the code that I dont understand. The LineIn = A then a couple lines down A = LineIn, seems like it would create an infinite loop.

'************************************************* ***************
'* Name : Timecode.BAS *
'* Author : Brian Critchlow & Brian Taylor *
'* Notice : Copyright (c) 2007 Brian Critchlow & Brian Taylor *
'* : All Rights Reserved *
'* Date : 10/11/2007 *
'* Version : 1.0 *
'* Notes : PIC 16F737 *
'* : *
'************************************************* ***************
TRISB = %00000000 'portb output
TRISC = %11111111 'portc input
ADCON1 = %11111111 'all ports digital

define OSC 4 '4mhz oscillator

DEFINE LCD_DREG PORTB ' Set LCD Data port
DEFINE LCD_DBIT 0 ' Set starting Data bit (0)

DEFINE LCD_RSREG PORTB ' Set LCD Register Select port
DEFINE LCD_RSBIT 4 ' Set LCD Register Select bit

DEFINE LCD_EREG PORTB ' Set LCD Enable port
DEFINE LCD_EBIT 6 ' Set LCD Enable bit

DEFINE LCD_BITS 4 ' Set LCD bus size (4 or 8 bits)
DEFINE LCD_LINES 2 ' Set number of lines on LCD
DEFINE LCD_COMMANDUS 2000 ' Set command delay time in us
DEFINE LCD_DATAUS 50 ' Set data delay time in us
pause 1000 '1 second delay

'-------------------Begin timecode section---------------------------
' an untried attempt at decoding the 2400 bps data stream used in the
' SMPTE LTC timecode system
'
'Defines go here

' Hardware definitions
LineIn var portC.2 'or whatever moves you

' Software definitions
A var byte
B var byte
C var byte
Msg var byte[8] ' up to 64 bits of timecode data
Valu var bit ' data bit from the biPhase data stream
Width var byte ' the number of 20 uSec chunks in the bit period
' 2400 bps is approx 416 uSecs per bit
' a ZERO should return a count of approx 20
' a ONE should yield a count of approx 10
Pattern var word ' this must match the SYNC pattern to start

'************************* Initialise block *************************
FlashLEDs: ' show em we are alive, etc
LCDOUT $FE, 1, "TC ", $FE, $C0, "Reader" 'tag line
pause 1000 '1 second delay

goto start 'jump subroutines at startup

'************************* Subroutines ****************************
FindBit:
' This extracts the 0 or 1 data bits from the incoming data stream
width = 0
FindEdge:
a = linein
pauseus 20
width = width + 1
if width > 14 then foundzero ' can't be a ONE - must be a ZERO.
' important that we exit early so we have approx 100 uSecs for
' other tasks before the next data transition. Allow for jitter
' and don't make the width comparison too tight
if linein = a then findedge
' sample a second time - repeat if no change
FoundOne:
LCDOUT $FE, 1, "Found ", $FE, $C0, "1" 'tag line
pause 500 '1 second delay
'at this point we have a transition under 15 counts so must be a ONE.
valu = 1
goto findbitdone
FoundZero:
LCDOUT $FE, 1, "Found ", $FE, $C0, "0" 'tag line
pause 500 '1 second delay
valu = 0
FindBitDone:
return

'***************************** MAIN ******************************
START:
FindSync:
' The values of the sync bits are fixed as 0011 1111 1111 1101
' Make a sliding window comparator by sliding the bits in the Pattern word
' up one place and adding the latest bit to the end and comparing this
' with the Sync word. NOTE the MSB/LSB might need swapping end for end.
gosub findbit
pattern = pattern << 1 + valu ' slide up one place and add latest bit
if pattern = %0011111111111101 then foundsync
goto findsync 'get one more bit & check again - keep doing it until a match
FoundSync:
LCDOUT $FE, 1, "Found ", $FE, $C0, "Sync" 'tag line
pause 500 '1 second delay
GetData:
for b = 0 to 5 ' get 6 message bytes - bytes 6 & 7 are sync - so skip
for a = 0 to 7 ' get 8 bits in each message byte
gosub findbit
c.0[a] = valu ' fill the 8 bits in the byte
' MAY need a tweak to get MSB/LSB sense correct
next a
msg[b] = c
next b
' at this point you should have 6 bytes of message that needs
' to be broken down into the various data blocks per the
' SMPTE LTC specification

DoWhatever:
' unpack the nibbles you are interested in.
LCDOUT $FE, 1, Msg[0], $FE, $C0, Msg[1]

goto start