Dawn CONTROL-1500A Manual page 75

CONTROL-1500A Single Axis Antenna Controller Appendix D The RCI RS422 Interface Spec 68
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 RC-2000A, 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.
All permissible transitions between states are represented graphically by arrows between
them. Each transition is qualified by a condition that must be true in order for the transition to
occur. The device will remain in its current state if conditions, which qualify transitions leading
to other states, are false, or conditions that qualify pseudo-transitions are true. A pseudo-
transition is a transition that occurs within the same state and is represented graphically by
arrows leaving from and arriving at the same state. Table 1 describes mnemonics used to
identify transitions in the state diagram.
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