4-1
Chapter 4. REMOTE CONTROL
4.1 I
NTRODUCTION
This document describes the protocol and message repertoire for remote monitor and control of
the XSAT Outdoor terminal.
The electrical interface is either an RS-485 multi-drop bus (for the control of many devices) or an
RS-232 connection (for the control of a single device), and data is transmitted in asynchronous
serial form, using ASCII characters. Control and status information is transmitted in packets, of
variable length, in accordance with the structure and protocol defined in later sections.
4.1.1 RS-485
The RS-485 interface is provided at the 19-pin circular J5 connector. The interface is a 4-wire
RS-485 interface using the pin out shown in Table 4-1. Since a half-duplex communication
protocol is used, the +Tx and +Rx as well as the –Tx and –Rx signals can be tied together at the
user end to support a 2-wire interface. The RS-485 driver is only active during transmission and
is tri-stated when not is use.
Table 4-1. RS-485 Interface
Pin Signal Name I/O
Notes
A
RS--485 +Rx
Input
XSAT Receive line
B
RS--485 –Rx
Input
XSAT Receive line complement
C
RS--485 +Tx
Output
XSAT Transmit line
D
RS--485 –Tx
Output
XSAT Transmit line complement
T Ground
Passive
