AC7A/B User’s Guide
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Setup
Although this issue can be addressed using a 4-wire RS-485 wiring system, the easiest, simplest way to address this
issue is to setup each of the AC7A/Bs for 2-wire RS-485 mode, described in the previous section. However, the
discussion and diagrams of 2-wire RS-485 mode assumes there will only be one AC7A/B on the link. When using
multiple AC7A/Bs on one link, biasing and termination jumpers will need to be set differently.
Biasing
Be sure to apply biasing at only one location on the RS-485 link. When the AC7A/B is configured for 2-wire
RS-485 mode, biasing is applied by installing the B1 and B3 jumpers. These jumpers should only be installed on one
AC7A/B on the link; they should be removed for all other AC7A/Bs on the link.
Termination
Be sure to apply termination at both ends of the RS-485 link. When the AC7A/B is configured for 2-wire RS-485
mode, termination is applied by installing the B2 jumper.This jumper should be removed for all other AC7A/Bs on
the link (i.e., all AC7A/Bs that are not at the physical ends of the RS-485 link).
Wiring and Related Jumpers
When the AC7A/B is configured for 2-wire RS-485 mode, the transmitter (TO terminals) and receiver (FO terminals)
are connected together (see the wiring diagram in the previous section). Because of this, jumpers B4, B5, and B6
should be removed on all AC7A/Bs.
Additional Jumpers
In addition, since the RTS and CTS pairs are not used on the RS-422/485 side of the AC7A/B, it is best to install
jumpers C2, C4, C5, and C6 to prevent spurious LED activity.
