Manual

Configuration CP346

P R E L I M I N A R Y

4.1.2 RS422/485 Termination Jumpers

The CP346 offers onboard two 120 ohm termination resistors per channel, which can be used

to terminate the differential line pairs in case the serial channel is a beginning or end node of a

RS422/485 network.

4.1.3 Handshake Control in Half Duplex RS485 Mode

In the two-wire half-duplex RS485 mode a handshake mechanism is necessary to prevent the

sending and receiving of data at the same time over the same RS485 cabling. Otherwise a data

crash would occur.

For the handshake mechanism the driver enable (DE) and receiver enable (RE) signals of the

RS422/485 transceivers must be managed. This is achieved with the help of the CPLD logic

receiving the RTS or DTR serial signals as inputs and generating the DE and RE signals as

outputs for the transceivers. The Oxford OX16PCI954 driver uses the DTR signal for such con-

trol, but there may be other software on the market, where the RTS signal executes this task.

Therefore on the CP346 and CP346-OPT the input signal to the CPLD is configurable as

shown in the following tables:

Table 4-3: Termination Jumper Settings for CP346 and CP346-OPT

Ch.0 Ch.1 Ch.2 Ch.3 Setting Description

J7 J6 J3 J2

Open (default) Termination between TRXD± in half duplex mode or TXD± in full

duplex mode

Open: No 120 ohm termination

Set: 120 ohm term. between differential lines

Set

J8 J5 J4 J1

Open (default) Termination between RXD± in full duplex mode

Open: No 120 ohm termination

Set: 120 ohm term. between differential lines

Set

Table 4-4: RS485 Transceiver Control for CP346

Channel0 Channel1 Channel2 Channel3

R67 R68 R69 R70 R65 R66 R63 R64

DTR signal controls

DE/RE (default)

Open Set Open Set Open Set Open Set

RTS signal controls DE/RE Set Open Set Open Set Open Set Open

Table 4-5: RS485 Transceiver Control for CP346-OPT

Channel0 Channel1 Channel2 Channel3

R4 R3 R52 R48 R47 R26 R22 R20

DTR signal controls

DE/RE (default)

Open Set Open Set Open Set Open Set

RTS signal controls DE/RE Set Open Set Open Set Open Set Open