RS422 machine control
“machine control” generally refers
to remote control of television production or
broadcast equipment, typically
VTR’s, VCR’s, switchers, etc. More often than not, this involves
an RS-422 serial connection between
the controller and the controlled device. Although multimachine
(multidrop, addressable) protocols
are sometimes used, mainly in audio editing suites,
most installations are
point-to-point.
The controller may be a dedicated
VTR controller, an editing system, a workstation or any other
device capable of sending out the
serial control messages as required. The serial link baud rate
is often 38400 bits/sec., although
some new telecine equipment works at much higher rates.
Typically, the controller will issue
a command (“Play”), whereupon the controlled equipment will
return an ACK and commence playing .
If the command has been incorrectly formed, or some
other error causes the equipment to
reject it, a NACK will be returned, sometimes with a byte
indicating the reason why.
