rtd cpuModules CME34BT, User Manual, Page: 49 / 110

BDM-610000088 Rev A Chapter 3: Connecting the cpuModule 41
RS-485 Mode Pinout
Table 15 provides the serial port connector pinout when RS-485 mode is enabled
Facing the serial port connector, the pinout is:
Table 15 Serial Port in RS-485 Mode
Pin Signal Function In/Out DB-9
1 D– Data (–) in/out 1
2 — Reserved — 6
3 D+ Data (+) in/out 2
4 — Reserved — 7
5 — Reserved — 3
6 — Reserved — 8
7 — Reserved — 4
8 — Reseved — 9
9 GND Signal Ground — 5
10 GND Signal Ground — —
9 7 5 3 1
GND Rsvd Rsvd D+ D-
GND Rsvd Rsvd Rsvd Rsvd
10 8 6 4 2
WARNING The pinout of the COM ports in RS-485 mode is not compatible with previous
generations of RTD cpuModules.
Note When using the serial port in RS-485 mode, the serial transmitters are enabled and
disabled under software control. The transmitters are enabled by manipulating the Request
To Send (RTS*) signal of the serial port controller. This signal is controlled by writing bit 1
of the Modem Control Register (MCR) as follows:
•
If MCR bit 1 = 1, then RTS* = 0, and serial transmitters are disabled
•
If MCR bit 1 = 0, then RTS* = 1, and serial transmitters are enabled
Note For more information on the serial port registers, including the MCR, refer to the
Serial Port Programming reference in Appendix D.