Comtech EF Data CRS-300 - Manual (Page 217)

7–1
Chapter 7. SERIAL-BASED REMOTE PRODUCT
MANAGEMENT
7.1 Overview
The CRS-300 1:10 Redundacy Switch serial remote product management interface is an electrical interface that is either an EIA-485
multi-drop bus (for the control of multiple devices) or an EIA-232 connection (for the control of a single device). The interface transmits
data in asynchronous serial form, using ASCII characters. This data consists of control and status information, transmitted in packets of
variable length in accordance with the structure and protocol explained later in this chapter.
See Sect. 3.2.1.3 Remote Control Connector, DB-9M in Chapter 3. SWITCH CONNECTORS AND PINOUTS for the EIA-232 and
EIA-485 connector pinouts Table 3-2.
7.2 EIA-485
For applications where multiple devices are to be monitored and controlled, a full-duplex (or 4-wire plus ground) EIA-485 is preferred.
Half-duplex (2-wire plus ground) EIA-485 is possible, but is not preferred. In full-duplex EIA-485 communication, there are two
separate, isolated, independent, differential-mode twisted pairs, each handling serial data in different directions.
It is assumed that a 'Controller' device (a PC or dumb terminal) transmits data in a broadcast mode via one of the pairs. Multiple
'Target' devices are connected to this pair, and all simultaneously receive data from the Controller. The Controller is the only device
with a line-driver connected to this pair – the Target devices have only line-receivers connected.