Grass Valley Switcher Products - Manual (Page 102)

102 Switcher Products — Protocols Manual
Section 3 — Peripheral Bus II Protocol
Query Command
The controlling device sends a Query command to the selected controlled
device to determine whether it is connected to the bus and operating. The
selected controlled device should return a Query response within four (4)
television fields. If no response is received within that time, the controlling
device will assume that the controlled device is not connected or is unable
to answer due to minimum implementation of the protocol.
The format of the Query command is:
Qdd<cr>
• The first byte is the ASCII keyword for Query, Q (51H).
• Next a two-byte field of ASCII characters (dd) representing a hex
number is sent that corresponds to the controlled device number
(00H-17H).
• A carriage return ends the message.
Query Response
A controlled device sends a Query response to the controlling device in
response to a Query. The Query response must be returned within four (4)
television fields, otherwise the controlling device will assume that the con-
trolled device is not there or is not capable of responding.
In order to provide the Query response, the controlled device must enable
its RS-485 drivers, transmit the response, and then disable its drivers. It is
essential that the controlled device do this cleanly, with the driver enabled
only long enough to transmit the message. It is also very important that the
controlled device leave its drivers disabled at all other times.
The format for the Query Response is:
Q[device type]<cr>
• The first byte is the ASCII keyword for Query, Q (51H), the same as the
Query command.
• Next an ASCII alphanumeric field of up to 16 characters is sent. These
characters, which are treated as raw data, identify the device. For
example, “GVG HOR BUS 35” indicates a Grass Valley Group Horizon
routing switcher bus number 35.
• A carriage return ends the message.