
Overview of Momentum Option Adapters
870USE10110 July 2004 67
Modbus Port 2 Modbus port 2 is a general-purpose asynchronous serial port with user-selectable
RS232/RS485 slave functionality. The choice between RS232 and RS485 is made
in the software.
Auto-Logout
Feature On
Modbus Port 2
If the RS232 port is chosen, auto-logout is supported. If a programming panel is
logged into the CPU via the serial port and its cable gets disconnected, the
processor adapter automatically logs out the port. This auto-logout feature is
designed to prevent a lock-up situation that could prevent other host stations from
logging in on other ports.
Auto-logout is not available for any RS485 port, including the RS485 option on the
serial option adapter. The user must log out of the processor using the programming
software.
Pinouts for
Modbus Port 2
The 172 JNN 210 32 serial option adapter uses the following pinouts:
Note: When this option adapter is assembled with a 171 CCS 780 00 processor
adapter or a 171 CCC 780 10 processor adapter (with built-in Modbus port 2), the
Modbus port 2 on the option adapter is electrically disabled. The TOD clock and
the battery backup on the option adapter remain functional.
Pin For RS232 For RS485
1DTR RXD -
2DSR RXD +
3TXD TXD +
4RXD
5 signal common signal common
6RTS TXD -
7CTS
8 cable shield cable shield
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