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MBT-5003 L-Band Up/Down Converter System
Appendix A
In the other direction: On the other pair, each Target has a tri-state line driver connected; 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; each time the Controller transmits, the address of the intended recipient Target is included in a framed 'packet' of data. 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:
•
Two differential pairs - one pair for Controller-to-Target, one pair for Target-to-Controller.
•
Controller-to-Target pair has one line driver (Controller), and all Targets have line-receivers.
•
Target-to-Controller pair has one line receiver (Controller), and all Targets have tri-state drivers.
A.3
Basic Protocol
With EIA-485 mode, all data is transmitted as asynchronous serial characters, suitable for transmission and reception by a UART. The
asynchronous character format is 8-N-1 (8 data bits, no parity, one stop bit). The supported baud rates are 2400, 4800, 9600, 19200, and
38400 baud.
All data is transmitted in framed packets. The Controller is assumed to be a PC or ASCII dumb terminal that is in charge of the process of
monitor and control. The Controller is the only device that is permitted to initiate, at will, the transmission of data. Targets are only
permitted to transmit when they have been specifically instructed to do so by the Controller.
All bytes within a packet are printable ASCII characters, less than ASCII code 127. In this context, the Carriage Return and Line Feed
characters are considered printable.
All messages from Controller-to-Target require a response, with one exception: This will be either to return data that has been requested by the
Controller, or to acknowledge reception of an instruction to change the configuration of the Target.
A–2
Revision 1
MN-MBT5003
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