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TS-2200 User's Manual
available in a screw-down terminal block. See the table below for pin-outs Note: the correct jumper
must be installed. See the next table for details.
Position (with terminal strip facing you)
Silk-screen Label
Half-duplex Usage
Full-duplex Usage
For full duplex (RS-422) operation, a twisted pair is used for
receiving and another twisted pair is used for transmitting.
The RS-485 transmitter is typically enabled continuously
(RTS asserted), since the separate transmit and receive
twisted pairs remove problems with data loop-back. The
full-duplex receiver inputs are available on the terminal
block (see the table above). Note: the correct jumper must
be installed - see the table below for details.
Fail-safe bias resistors are used to bias both the TX pair
and the RX pair to the correct state when these pairs are
not being actively driven. This is an important consideration,
since in a typical RS-485 installation, the drivers are
frequently tri-stated. If fail-safe bias resistors are not
present, the 485 bus will be floating and very small amounts
of noise can cause spurious characters at the receivers. A
1.2 KOhm resistor is used to pull the TX+ signal to 5V and
another 1.2 KOhm resistor pulls the TX- signal to ground.
The RX+ and RX- signals are biased in the same manner.
Termination resistors are also required for reliable
operation particularly when running long distances.
Termination resistors should only be installed at each end
of a RS-485 transmission line pair. In a multi-drop
application where there are several drivers and/or receivers
attached, only the devices at each end of the
transmission line pair should have termination
resistors.
Installing JP4 adds a 100 Ohm termination resistor to
the RX pair while JP5 adds a 100 Ohm termination
resistor to the TX pair.
When the RS-485 option is installed, jumpers JP6 and
JP7 select which receiver is fed to the COM1 UART.
Only one (or neither) of these jumpers should be
installed at a time!
A read at I/O location 76h bit 0 will return a "1" when
the RS-485 option is installed.
5.4 Automatically Enabled RS-485
In most RS-485 applications, the transmitter is enabled while sending data and disabled (tri-stated)
when not. This allows for an inexpensive 'network' of multiple devices, all using a single twisted pair to
communicate. Enabling and disabling the RS-485 transmitters can be done in software by asserting
and deasserting RTS. This can be difficult to implement and bug prone.
Left
TX+
TX-
TX+ / RX+
TX- / RX-
TX+
TX-
Table 1 - RS-485 Signals
I/O
Address
76h
76h
77h
Table 2 – TS-2100 Control Registers – All signals
8
Technologic Systems
Center
GND
RX-
GND
Not Used
GND
RX-
RS-485 Quick start procedure:
1. The RS-485 option must be
installed
2. Install JP6 or JP7 to enable Half or
Full duplex RS-485 operation
3. Attach the RS-485 cable to the 5-
pin terminal strip connector.
4. Set the COM1 UART serial
parameters (baud rate, data, parity,
and stop bits, interrupts, etc).
5. To transmit data, assert RTS and
write the data to the UART
6. To receive data, deassert RTS and
read the data from the UART
Jumper
Receiver Source
JP6
Full-duplex RS-485
JP7
Half-duplex RS-485
neither
RS-232
Table 3 - COM1 Receiver Source
R / W
Bit 0 Description
Read
RS-485 option
0 = Not installed
1 = Option installed
Write
RS-485 control
0 = use RTS enabled RS-485
1 = enable automatic RS-485
Read
Returns status of TX485EN pin
are R/W through bit 0 of the address
Right
RX+
Not Used
RX+
11/06/2000
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