Delta RMC101 - Manual (Page 494)

RMC100 and RMCWin User Manual
5-244
in the RMC SERIAL configuration.
The RMC RS-232 communications require only three conductors in the cable: RxD, TxD, and
GND. A five-conductor cable must be used if the CTS and RTS signals are used.
Delta recommends that a shielded cable be used to limit susceptibility to outside electrical
interference.
Cable Length
One of the characteristics that limit the length of an RS-232 cable is capacitance. Most cables
have a capacitance rating in pF/ft. The maximum distance that you can reliably transmit signals
can be determined by answering a few questions and plugging the answers into the following
formula:
MaxLength = 2400 pF / ( C + ( Shield * C ) )
Where: Shield = 2 for shielded cable and 0.5 for unshielded cable
C is the capacitance rating of the cable in pF/length
2400 pF is derived by taking the maximum capacitance specified by ANSI/TIA/EIA-232-F
(2500 pF) and subtracting 100 pF for the input capacitance of the receiver
If you need to run your communications farther than allowed by this formula, then you must either
use a cable with lower capacitance or use RS-422 or RS-485.
Example:
The cable that is being used is shielded and has a capacitance of 15 pF/ft.
MaxLength = 2400 pF / ( 15 pF/ft + (2 * 15 pF/ft) )
= 2400 pF / ( 45 pF/ft )
= 53.3 ft
5.5.2.6 RS-422/485 Wiring for the RMC SERIAL
Connectors
Both RS-422 and RS-485 use the 6-pin connector block on the RMC SERIAL module. The pin-
out is the same for RS-422 as 4-wire RS-485:
RS-422/485 (4-wire) Pin-out
Pin RS-422/485 (4-wire) Function
1 Tx A (-)
2 Tx B (+)
3 Rx A (-)
4 Rx B (+)
5 Common
6 Case
Two-wire RS-485 uses the following pin-out: