289 Programmable Hardware Manual (PHM)
© Tibbo Technology Inc.
When unconnected, FD/-HD defaults to HIGH, while -232/422-485 defaults to LOW.
This means that the RS232 mode will be selected.
In the RS232 mode the port has RX, TX, RTS, CTS, DTR, and DSR signals. This is
the full-duplex mode.
In the RS422 mode the port has +/-RX, +/-TX, +/-RTS, and +/-CTS signal pairs.
This is the full-duplex mode.
In the RS485 mode the port has only +/-RX and +/-TX signal pairs. This is the half-
duplex mode, so you can connect +RX to +TX, and -RX to -TX. This will allow your
system to communicate over a single twisted pair. Direction control is through the
RTS line -- the line shall be LOW for data input and HIGH for output.
For "normal" RS232/422/485 applications, this Tibbit has to be connected to the TX
and RX lines of the CPU's UART (see [SER]). Planning to use RTS/CTS flow control
as well? An interrupt line must be available, too (see [INT]).
Combining this Tibbit with the "C" device #19 (DB9M connector) will create a serial
port with the following pin assignment on the DB9M:
The above pin assignment is the same we use on all our devices with the universal
port (for example, see the serial port of the DS1102).
You can also combine the RS232 Tibbit with #20 (9 terminal blocks).
LEDs
There are eight LEDs: five red and three green. Red LEDs are connected to TX, RTS,
DTR, FD/-HD, and -232/422-485 lines. Green ones are for RX, CTS, and DSR. All
LEDs are buffered (with logic gates) and light up for the LOW state of control lines.
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