Grass Valley 2200 - Manual (Page 111)

5-21
Other Command Specifics
Other Command Specifics
The bulk of the communications used for the switcher/DPM interface is via
parametric interchange, as indicated in Appendix B. This section tabulates other
commands used by the switcher/DPM interface.
Currently, the only other communications is the exchange of an on line event
while communications are initiated. The DPM must transmit an on-line event and
respond to one sent by the switcher with an appropriate return code message.
Transmission Media and Protocols
The switcher/DPM interface is designed as a point-to-point link. Messages are
delivered in an HDLC-like frame consisting of an 8-bit opening ßag, a variable-
length data Þeld, a 16-bit CRC, and an 8-bit closing ßag. Within the transmission
frame, messages are delivered via the data Þeld.
A 307.2K baud FM0 synchronous serial link with imbedded clock is used for
deterministic communications. Data rate and frame format are not adjustable.
HDLC is a synchronous protocol with built-in mechanisms for error detection and
packet detection.
Not all UARTs support this protocol. Those that do handle the packetization, zero
stufÞng and CRC insertion/detection. A Motorola 68302 along with a 68195 are
used in the switcher for this interface. A Motorola 68360 or Zilog 8030 or 8530 also
support this protocol.
Unlike asynchronous protocols, communications is frame (packet) based. A
transmit underrun is not permitted in a synchronous protocol and will abort the
transmission of the frame and the receiver will discard it.
The physical connection between the switcher and the digital effect device (DPM)
is point to point with two RS-422 pairs, one for each direction.
The connector provided for this interface is a female DB-9. It is located on the rear
of the switche frame and labled ÒA1Ó. The pinout is shown below.
Table 5-11. Return Code Message Data
Function Pin
Tx + (switcher to DPM) 3
Tx - 8
Rx + (DPM to switcher) 7
Rx - 2
Ground 1, 4, 6, 9