Write command, Write response – Grass Valley Switcher Products User Manual
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Switcher Products — Protocols Manual
Section 3 — Peripheral Bus II Protocol
Write Command
The controlling device sends a Write command to the selected controlled
device in order to transmit data to the controlled device.
The format of the Write command is:
Wddrrr[reg data]
•
The first byte is the ASCII keyword for Write, W (57H).
•
Next a two-byte field of ASCII characters (dd) representing a hex
number is sent that corresponds to the controlled device number
(00H-17H).
•
Next three ASCII characters are transmitted which represent the hex
number of the register which the controlling device wants to write to
(000H-FFFH).
•
Next the register number, up to 16 ASCII characters, which are treated
as raw data, may be sent.
•
A carriage return ends the message.
Write Response
A controlled device sends a Write response to the controlling device in
response to a Read command. The Write response must be returned within
four (4) television fields, otherwise the controlling device will assume that
the controlled device is not there or is not capable of responding.
In order to provide the Write 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 of the Write response is:
Wddrrr[reg data]
•
The first byte is the ASCII keyword for Write, W (57H), the same as the
Write command.
•
Next a two-byte field of ASCII characters (dd) representing a hex
number is sent that corresponds to the controlled device number
(00H-17H).
•
Next three ASCII characters (rrr) are transmitted representing the hex
number of the register whose contents are to be read (000H-FFFH).
•
Next up to 16 ASCII characters may be sent. The controlling device will
treat these characters as raw data.
•
A carriage return ends the message.