Visca Message Format - Cisco TelePresence PrecisionHD 1080P 12x User Manual

Cisco TelePresence PrecisionHD Camera
Contents Introduction
The VISCA™/RS–232
control protocol
When interfacing to the PrecisionHD 1080p
12X and the PrecisionHD 1080p 4X, the
codec uses an RS-232 control interface that
resembles the Sony VISCA™ protocol.

VISCA message format

A particular command is recognized by the
message information after the address byte.
Message Format
Commands are initiated from the host (i.e. the
codec or any other external controller) to the
camera.
After a camera has been issued a command,
the camera will generate a response.
Commands and responses (messages) have
the following format:
•
Address byte (1)
•
Message bytes (1..14)
•
Terminator byte (1)
See the illustration for details.
D14640.03 PrecisionHD 1080p-720p Camera User Guide TC4.0, November 2010.
© 2010 Cisco Systems, Inc. All rights reserved.
The physical interface Connecting the camera
The RS232 Message format
Packet (3 to 16 bytes)
Address Message (1 to 14 bytes)
Byte 1 Byte 2 Byte 3
1 0
LSB
Sender's Receiver's
address address
The minimum length of any command or response is 3 bytes:
1. Address byte (1): Let us assume there is one host, i.e. the codec (the host is the unit controlling
the camera). The host has address 0. The four least significant bits of the address byte contain
the address of the receiver. In the case of a broadcast message, the receiver address must
be set to 8. When we are operating a single camera, the address is 1. Hence, address bytes in
messages from the host are 0x81, and messages from the camera to the host are 0x90 (the
protocol allows for up to 7 cameras).
2. Message bytes (1..14): Any number of bytes containing the actual message information. Bytes
may have any value in the range 0...254. The value 255 (i.e. hexadecimal FF) is reserved for the
terminating byte.
3. Terminator byte (1): All messages must be terminated with a byte containing all 1's, i.e. decimal
255 (or hexadecimal FF).
Video output formats
Terminator
...
1 1 1 1 1 1 1 1
20
PrecisionHD Camera User guide
Daisy chaning
Command and response exchange
When the camera receives a command, it
responds with either:
•
Completion message: 90-5Y-FF
Returned by camera when execution of
commands and inquiries are completed.
•
Error packets: 90-6Y-..-FF
Returned by camera instead of a
completion message when command or
FF
inquiry failed to be executed.
•
General error messages, unless otherwise
specified:
•
90-6Y-01-FF Message length error
(>14 bytes)
•
90-6Y-02-FF Syntax error
LSB
•
90-6Y-03-FF Command buffer full
•
90-6Y-04-FF Command cancelled
•
90-6Y-05-FF No socket (to be cancelled)
•
90-6Y-41-FF Command not executable
•
Y = socket number
A camera may contain two buffers so that
two commands, including the command
being executed, can be received.
The PrecisionHD 1080p
NOTE:
camera supports a single socket only.
Consequently, the Y always assumes the
value Y = 0.
Exceptions to these rules:
•
An Initialize message will respond as
indicated in the Table of Commands (this
message is in fact a broadcast message,
and any unit other than the host receiving
the broadcast message must pass it on).
•
Do not route commands or replies that are
longer than 16 bytes through Sony cameras.
The easiest way to avoid this is to put the
Cisco cameras first in the chain. Commands
and replies that are longer than 16 bytes are
clearly marked below.
Appendices Appendices
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