Research Concepts RC2500 - Manual (Page 84)

RC2500 Antenna Controller Appendix E RC2500 Comm Protocol 77
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Appendix E – RC2500 Communications Protocol
Revision History
12/8/97 Original communications protocol for the RC2500 derived from the RC2000C v1.1x document.
Overview
The RC2500 command set conforms to the SA Bus protocol originally defined by Scientific Atlanta. This
file describes the commands used to implement the SA bus remote interface for the RC2500 antenna
controller. See the SA Bus specification included with RC2500 manual for a complete description of the
protocol.
Communications Parameters
The controller’s baud rate and address must be set before communication with a host is possible. These
quantities can be specified in the CONFIG mode. The range of acceptable addresses is 49 to 111. The
possible baud rate values are 300, 600, 1200, 2400, 4800, or 9600. The usual SA Bus baud rate is 9600.
For completeness, the transmission parameters are repeated here: 7 data bits, even parity, 1 stop bit.
RC2500 Online/Offline
To enable REMOTE mode on the RC2500, the internal remote$mode$enable$flag must be set. This flag
is set at the Remote Mode Enable prompt in CONFIG mode. When this flag is set, REMOTE mode can
be entered in two ways. One way REMOTE mode can be activated is by depressing the mode button.
REMOTE mode can be found just after AUTO mode. REMOTE mode will also be activated when a valid
command arrives via the serial port. Certain commands can be processed by TRACK mode.
If the remote$mode$enable$flag is FALSE and a valid command arrives via the serial port, the offline
reply is sent to the host. Here is the format of the offline reply...
byte 0 ACK
byte 1 A where A is the RC2500 address
byte 2 'CC' the command code of the message which triggered this reply.
byte 3 'F' ASCII 'F', for offline.
byte 4 ETX
byte 5 'checksum the checksum. The checksum character is simply the bit-by-bit
exclusive OR of all characters in the message starting with the
STX character through the ETX character.
RC2500 Unrecognized Commands - NAK Reply
If an unrecognized command arrives (one whose command code is either unknown or whose length is
not compatible with the given command code, but which has the correct address and checksum), a NAK
reply is sent to the host. The format of the NAK reply is ...
byte 0 NAK
byte 1 A where A is the RC2500 address
byte 2 'CC' the command code of the unrecognized message.
byte 3 ETX
byte 4 checksum
Device Type Query Command
The SA Bus specification requires that command character 30h must trigger the return of the six
character device type string. The message format for this query will be ...
byte 0 STX
byte 1 A where A is the RC2500 address
byte 2 30h 30 hex - the device type query command code
byte 3 ETX