Alcorn Mcbride 1756-Show I/O, User Manual, Page: 18 / 33

12 Using the Module as a SMPTE Generator
The SMPTE generator follows a simple process to generate time code. Each
frame, the module performs these tasks:
1. Convert the current time to a string of 80 bits and if the generator is not
muted, send those bits out the SMPTE output.
2. If the STOP bit has changed from a zero to a one, switch the generator from
RUNNING to IDLING.
3. If the RUN bit has changed from a zero to a one, switch the generator from
IDLING to RUNNING.
4. If the SET bit has changed from a zero to a one, replace the current time
with the user’s new time code, otherwise, add one frame to the current time
if running or leave the current time unchanged if idling.
5. If the current time matches the Loop End time, replace the current time with
the Loop Start Time if the Loop bit is set (one), or switch from RUNNING
to IDLING if the Loop bit is clear (zero).
6. If the unit is idling and the MUTE bit is set, mute the SMPTE output.
7. Make the time code available to the PLC through the Input File.
Configuring the Generator
The 1756-Show I/O generator is entirely controlled by words in the PLC Output
File. See the Module I/O Space chapter for a diagram of the Output File.
Operating Mode
When the MODE bit is set (one), the module will generate SMPTE time code
internally. When this bit is clear (zero) the module will read external SMPTE
time code.