Rockwell Automation 2755-DM9, -DM9E High Speed Decoder - Manual (Page 88)

Chapter 6
Communicationg With a Host
6–6
Figure 6.4
Communications in an RS-485 Network
See Note #1
HOST Port on Decoder
7
14
15
RS-485 + Transmit/Receive
SHIELD
Shield
12
13
B RS-485 + Transmit/Receive
A RS-485 - Transmit/Receive
Host Device
Exact pin designations depend on
specific host device used.
RS-485 - Transmit/Receive
COMMON COMMON
Note #1: One and only one of the devices on the network must have the
cable shield connected to chassis ground. This is accomplished by
connecting the shield to pin #1 instead of pin #9.
See Note #2
Note #2: The devices at each end of the network must have the line
termination enabled. You enable the line termination by connecting pins #12
and #13 together. Otherwise, pins #12 and #13 are left open.
9
RS-485 Line Termination
Cable : Use Belden 9842 or equivalent.
When you select the RS-485 interface during the decoder’s configuration, the
following parameters are fixed:
•
8 Data Bits
•
Even Parity
•
1 Stop Bit
Note: There are four RS-485 application modes:
•
RS485 PCCC-1: PCCC commands with write replies.
•
RS485 PCCC-2: PCCC commands without write replies.
•
RS-485 ASCII-1: ASCII commands with responses.
•
RS-485 ASCII-2: ASCII command without responses.
Refer to Chapter 8 for more information.