Impulse ACB-104 (3512) - Manual (Page 13)

Technical Description
Sealevel Systems ACB-104 Page 10
RS-530/422/485 Pin Assignments (At the DB-25)
Signal Name Pin # Mode
GND Ground 7
RDB RX+ Receive Data Positive 16 Input
RDA RX- Receive Data Negative 3 Input
CTSB CTS+ Clear To Send Positive 13 Input
CTSA CTS- Clear To Send Negative 5 Input
TXCB TXC+ Transmit Clock Positive 12 Input
TXCA TXC- Transmit Clock Negative 15 Input
RXCB RXC+ Receive Clock Positive 9 Input
RXCA RXC- Receive Clock Negative 17 Input
TDB TX+ Transmit Data Positive 14 Output
TDA TX- Transmit Data Negative 2 Output
RTSB RTS+ Request To Send Positive 19 Output
RTSA RTS- Request To Send Negative 4 Output
DTRB DTR+ Data Terminal. Ready Positive 23 Output
DTRA DTR- Data Terminal Ready Negative 20 Output
TSETB TSET+ Terminal Timing Positive 11 Output
TSETA TSET- Terminal Timing Negative 24 Output
Note: These assignments meet the EIA/TIA/ANSI-530A DTE Specification.
RS-530/422/485 Line Termination
Typically, each end of the RS-530/422/485 bus must have line-terminating resistors. A 120-ohm resistor is across
each RS-530/422/485 input in addition to a 1K ohm pull-up/pull-down combination that biases the receiver inputs.
The RS-530 specification calls for a 100-ohm 1/2-watt resistor between the signal ground and the chassis ground.
On the IBM PC, these two grounds are already connected together, therefore this resistor is omitted.