Alcorn Mcbride 1756-Show I/O, User Manual, Page: 20 / 33

14 Using the Module as a SMPTE Generator
Controlling 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.
Note: The 1756-Show I/O samples the control bits once per frame. Pulses of
less than 33 milliseconds will not activate the module properly.
Setting the Current Time
Whenever the SET bit transitions from a zero to a one, the SMPTE time in the
Set Time words will be loaded into the SMPTE generator’s output. The load
occurs at the next frame edge, so the time can be altered while the generator is
running or while it is idling. Any invalid entries, such as minutes greater than
59, will be treated as if the entry were zero. An error bit will be set in the Input
File to highlight the problem field.
Starting the Generator
Whenever the RUN bit transitions from a zero to a one, the generator switches
from IDLING to RUNNING. If the generator is already running, the rising edge
on the RUN bit has no effect.
Stopping the Generator
Whenever the STOP bit transitions from a zero to a one, the generator switches
from RUNNING to IDLING. If the generator is already idling, the rising edge
on the STOP bit has no effect.