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LPOD C-, X-, or Ku-Band Outdoor Amplifier / Block Up Converter (BUC)
Serial Interface Operation
5.3.2 EIA-485
For applications where multiple devices are to be monitored and controlled, 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) operation is summarized by its two differential pairs – one pair for Controller-to-Target, one pair for Target-to-
Controller:
• Controller-to-target pair – Pair has one line driver (Controller), and all Targets have line-receivers.
• Target-to-Controller pair – Pair has one line receiver (Controller), and all Targets have Tri-State drivers.
5.3.3 Basic Serial Protocol
Serial data can be transmitted and received by a Universal Asynchronous Receiver/Transmitter (UART).
Serial data is transmitted as asynchronous serial characters:
• Asynchronous character format is 8-N-1 (8 data bits, no parity, 1 stop bit)
• Baud rate can vary from 1200 through 57600 baud.
Serial data is transmitted in framed packets. All bytes within a packet are printable ASCII characters less than ASCII code 127
(DELETE). The Carriage Return and Line Feed characters are considered printable.
5–5
MN-LPOD
Revision 14
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