Sierra Video Manzanita 44VSCP - Manual (Page 7)

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Sierra Video Systems • P.O. Box 2462 • Grass Valley, CA 95945 • (530) 478-1000 • Fax (530) 478-1105
MODEL 44 INSTRUCTION MANUAL
SERIAL CONTROL PROTOCOL
The protocol is designed to use the 7-bit ASCII
character set, usually sent over a RS-232C serial
link at 9600 bps. The high-order data bit is ig-
nored on all received characters, and is 0 on all
transmitted characters.
The protocol is designed for use over a reliable
channel. Noisy channels such as modem connec-
tions over the telephone network should use an
error-checking and/or error-correcting protocol,
including such things as packet check sums or
CRC’s. Newer modems include such communica-
tion schemes as part of their normal operation,
and are recommended for these applications.
The protocol is designed to be compact, with few
characters required to cause switch changes to
occur. It is also designed to be human-readable
and thus easy to understand and use. Finally, it is
a modified subset of the existing SVS host proto-
col, allowing a degree of compatibility with those
existing systems.
Several different switch request commands are
defined, so that the one that is most compact for
any given switcher and application can be chosen.
All input, output, and level numbers begin at
number 1, not 0.
Command string
Commands are sent to a routing switcher in a
group called a command string. A command
string can contain zero or more commands,
limited only by the size of the receive buffer of
the switcher, which should be large enough to
hold a command string for setting the state of the
entire switcher matrix.
A command string consists of a leader, zero or
more commands, and a trailer. If a leader charac-
ter is encountered within the command string, the
command string up to that point is discarded and a
new command string is started. Once a complete
command string, up to the trailer character, is
received, the routing switcher executes the com-
mands within it.
Within the command string, certain ASCII charac-
ters may be present and are ignored: any ASCII
character whose code is less than or equal to the
SPACE character, and any whose code is greater
than the “~” (tilde) character. Alphabetic charac-
ters within the command string may be in either
uppercase or lowercase letters.
Just before the switcher begins executing a com-
mand string, it sends a leader character to the host.
After the command string has been executed, the
routing switcher returns the string “OK” (with a
single space character before and after the word
“OK”), followed by a trailer character (~) and a
CR character, to the host. This indicates that the
command has executed successfully. If an error
occurs within any command of a command string,
the remainder of the command string is ignored
and the switcher returns the string “ERROR”,
followed by a trailer character and CR character,
to the host. An error consists of an unknown
command name or bad arguments to a command.
Leader and Trailer.
“*” is a command string leader and “!” is a
command string trailer.
The simplest possible command string would be
“*!”, which consists of the leader and trailer
characters but no command between them. This
command string would generate the response “*
OK!” followed by “CR”. This can be useful for
verifying that the serial link to the switcher is
operational.
Following is the command set: