Omron CJ2 - A-4-4 Example of Recommended RS-232 C Wiring

Appendices
A-106
CJ2 CPU Unit Hardware User’s Manual
Precautions for Correct UsePrecautions for Correct Use
Use the special cables provided from OMRON for all connections whenever possible. If cables
are produced in-house, be sure they are wired correctly. External devices and the CPU Unit may
be damaged if general purpose (e.g., computer to modem) cables are used or if wiring is not cor-
rect.
We recommend the following wiring methods for RS-232C, especially in environment prone to noise.
• Use shielded twisted-pair cable for communications cables.
• Use a twisted-pair cable for each signal line and SG (signal ground) to connect the CPU Unit to a
communications partner. Also, bundle all the SG lines at the Unit and at the other device and connect
them together.
• Connect the shield line of the communications cable to the hood (FG) of the RS-232C connector at
the Unit. Also, ground the protective earth (GR) terminal of the Power Supply Units on the CPU Rack
and the CJ-series Expansion Racks to a resistance of 100 Ω or less. The following example shows
connecting SD-SG, RD-SG, RS-SG, and CS-SG for Serial Communications Mode using a twisted-
pair cable using the peripheral bus.
Note The hood (FG) is internally connected to the protective earth (GR) terminal on the Power Supply Unit
through the CPU Rack. FG can thus be connected by connecting the protective earth (GR) terminal on the
Power Supply Unit. The hood (FG) is also electrically connected to pin 1 (FG), but the connection resistance
between the shield and the FG is smaller for the hood. To reduce contact resistance between the hood (FG)
and the FG, connect the shield both to the hood (FG) and to pin 1 (FG).
A-4-4 Example of Recommended RS-232C Wiring
XM2S-0911-E
Hood
Shield
SG signal line
CPU Unit
External device
Signal
name
Pin
No.
Signal
name
SG signal lines
bundled together
Aluminum foil
2
3
4
5
9
1
SD
RD
RS
CS
SG
FG
FG
RD
SD
CS
RS
SG
FG
GR
CPU Unit
Power Supply Unit
Ground to 100 Ω
or less
Shield and GR connected
internally.
The hood will be grounded
if the GR terminal is grounded.