Research Concepts RC2500 - Manual (Page 81)

74 RC2500 Antenna Controller Appendix D The RCI RS422 Interface Specification
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Address Character
The device address must be a valid ASCII printable character between 31 and 6F in hex; thus, 63
addresses are possible. These are set in the controller in decimal format, or 49-111.
Command Character
The command character (CMD) immediately follows the device address and specifies one of several
possible commands for a particular device. See RCI document ‘RC2500 Command Set’ for a complete
description of these commands.
Check Character
The last character of any message is the check character (CHK). This character is simply the bit-by-bit
exclusive OR of all characters in the message starting with the STX character through the ETX character.
This forms a Longitudinal Redundancy parity check over the entire message.
Message Timing
The NAK or ACK reply does not signify that a function has actually taken place, but only that the
message was received and understood. The user should query the controller later to see if the command
was actually carried out, or is still in progress. Figure 5 shows the controller state diagram.
Command Restrictions
All slaves will respond to a command "0", 30 (hex), with 6 data bytes of ASCII characters in the following
form:
ACK ADDR 30 type D5 D6 ETX CHSUM
where type is RC2K for an RC2000A, RC1K for an RC1000A, 2KCA for an RC2000C for el-over-az
mounts, 2KCP for an RC2000C for polar mounts, 2KCE for az-over-el mounts, 2500 for the RC2500A,
25CA for an RC2500B for el-over-az mounts, 25CP for an RC2500B for polar mounts, and 25CE for az-
over-el mounts.
Slave State Diagram: Introduction
General Description. The slave State diagram (see Figure 5) presents the required protocol
implementation at the slave device that guarantees the proper transfer and processing of communication
messages sent by a Master controller.
State Diagram Notation. Each state that a slave can assume is represented graphically as a circle. A
single-digit number is used within the circle to identify the state.