454
External Controllers
© Tibbo Technology Inc.
DS1102
The DS1102 features a multi-mode, multi-channel RS232/422/485 port. Physically,
the port is implemented as a single DB9M connector.
The definition of RS422 and 485 modes
To avoid any misunderstanding of what the RS422 and RS485 modes are, let's clarify
that the term "RS422 mode" refers to full-duplex differential signaling interface with
at least RX and TX signals, and possibly with CTS and RTS signals. Each signal is
carried by a pair of "+" and "-" lines. The term "RS485 mode" refers to half-duplex
differential signaling interface with RX and TX lines, where each signal is also carried
by a pair of "+" and "-" lines. The RTS line of the serial port is used (within the
DS1102) to control the direction, so TX and RX lines can be combined (externally)
to form a two-wire bus that carries data in both directions. On a physical signal
level (voltages, etc.), there is no difference between the RS422 and RS485 -- they
are implemented in the same way.
RS422 and RS485 modes typically require termination circuits. No such circuits are
provided within the DS1102. A simple 120Ohm resistor (added externally) is
sufficient for the proper termination of one "+"/"-" pair.
Pin assignment
In the RS232 mode, the serial port of the DS1102 has 3 output and 3 input lines. In
the RS422 mode, you get 2 output and 2 input line pairs. The RS485 mode offer one
output line pair and one input line pair and these are not independent -- they
operate in the half-duplex mode).
Internally, the DS1102 has three independent serial ports. These are controlled
through the ser. object (see TIDE, TiOS, Tibbo BASIC, and Tibbo C Manual).
Each of those ports has its own TX and RX lines. These lines are implemented in
hardware and can't be "remapped". The following table shows how these RX and TX
lines are connected to the DB9M:
RS232
RS422
RS485
#1
<No connection>
TX2-
(output,
commonly RTS-)
<No connection>
#2
RX
(input)
RX-
(input)
RX-
(input)
#3
TX
(output)
TX+
(output)
TX+
(output)
#4
TX3
(output,
commonly DTR)
TX-
(output)
TX-
(output)
#5
Ground
Ground
Ground
#6
RX3
(input, commonly
DSR)
RX+
(input)
RX+
(input)