SMPTE Timecode reader

[docwisdom]

Hey all.

We are working in a production studio and all of our cameras are locked together by timecode. I would like a little timecode display in the control room so the logger is able to write down the timecode at varioius times.

Basically I just need to read the 80 bit digital signal and display it on an LCD display.

Its been a while since I coded anything so my picbasic is rusty. Maybe someone can check out these docs and get me on the right path.
I have the code to work the display, I just need a refresher on detecting start & stop bits, reading and splitting strings to appropriate variables.

thanks
-brian

http://www.philrees.co.uk/articles/timecode.htm#mod
http://www.philrees.co.uk/articles/timecode.htm#bcd


ps. right now using a 16F737 because I have one laying around.

[docwisdom]

ah, c'mon. i know someone wants to dive into this.

mr e, mel, you know you want to.

[docwisdom]

nothin yet. Darn.

[docwisdom]

??
anyone

[BrianT]

Untried but should get you started.

'************************************************* ***************
'* Name : BiPhase 01.BAS *
'* Author : Brian Taylor *
'* Notice : Copyright (c) 2008 Brian Taylor *
'* : All Rights Reserved *
'* Date : 29/01/2008 *
'* Version : 1.0 *
'* Notes : *
'* : *
'************************************************* ***************

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

' Hardware definitions
LineIn var portB.0 '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
PickNose: ' etc
ScratchBum: ' etc

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:
'at this point we have a transition under 15 counts so must be a ONE.
valu = 1
goto findbitdone
FoundZero:
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:

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.

goto start


HTH
Brian

[docwisdom]

Thanks brian
ill give it a stab and come back with a report ( and questions most likely)

-brian