Comtech EF Data CRS-500, Инструкция по установке и эксплуатации

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CRS-500 1:N Redundancy System
Revision 4
Serial Interface Operation 10–2 MN-CRS-500
10.2 Remote Control Protocol and Structure
The electrical interface is either an EIA-232 connection (for the control of a single device) or an EIA-485 multi-drop bus (for the control of many
devices). 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 this chapter.
10.2.1 EIA-232
This is a simple configuration in which the Controller device is connected directly to the Target via a two-wire-plus-ground connection.
Controller-to-Target data is carried, via EIA-232 electrical levels, on one conductor, and Target-to-Controller data is carried in the other
direction on the other conductor.
10.2.2 EIA-485
For applications where multiple devices are to be monitored and controlled, a full-duplex (or 4-wire) EIA-485 is preferred. Half-duplex
(2-wire) 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 there is a ‘Controller’ device (a PC or dumb terminal), which transmits data in a broadcast
mode via one of the pairs. Many ‘Target’ devices are connected to this pair, which all simultaneously receive data from the Controller. The
Controller is the only device with a line-driver connected to this pair – the Target devices only have line-receivers connected.
In the other direction, on the other pair each Target has a Tri-Stateable line driver connected, and the Controller has a line-receiver
connected. All the line drivers are held in high-impedance mode until one – and only one – Target transmits back to the Controller.
Each Target has a unique address, and each time the Controller transmits in a framed ‘packet’ of data, the address of the intended
recipient Target is included. All of the Targets receive the packet, but only one – the intended – will reply. The Target enables its output
line driver and transmits its return data packet back to the Controller in the other direction, on the physically separate pair.
EIA-485 (full duplex) summary:
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Two differential pairs: one pair for Controller-to-Target, one pair for Target -to-Controller.
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Controller-to-Target pair has one line driver (Controller), and all Target s have line-receivers.
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Target-to-Controller pair has one line receiver (Controller), and all Targets have Tri-State drivers.