Yokogawa Touch Screen GP20 - Manual (Page 13)

1-7
IM 04L51B01-17EN
Using Dedicated Commands (General)
1
2
App
• Four-wire system
Generally, a four-wire system is used to connect to a host device. In the case of a four-
wire system, the transmission and reception lines need to be crossed over.
Terminator (external) 120 Ω 1/2W or greater
#1
Do not connect terminators to #1 through #n-1.
RS-422/485
terminal on the GX/GP
#2 #n
(#n 32)
Terminator (external)
Host device
side
SG
RDB( + )
RDA( – )
SDB( + )
SDA( – )
FG
SG
RDB+
RDA–
SDB+
SDA–
(SG)
(RDB + )
(RDA – )
(SDB + )
(SDA – )
FG
SG
RDB+
RDA–
SDB+
SDA–
(SG)
(RDB + )
(RDA – )
(SDB + )
(SDA – )
FG
SG
RDB+
RDA–
SDB+
SDA–
(SG)
(RDB + )
(RDA – )
(SDB + )
(SDA – )
• Two-wire system
Connect the transmission and reception signals with the same polarity on the RS-422/485
terminal block. Only two wires are used to connect to the external device.
Terminator (external) 120 Ω 1/2W or greater
#1
Do not connect terminators to #1 through #n-1.
RS-422/485
terminal on the GX/GP
#2 #n
(#n 31)
Terminator (external)
Host device
SG
RDB( + )
RDA( – )
SDB( + )
SDA( – )
FG
SG
RDB+
RDA–
SDB+
SDA–
(SG)
(B+)
(A – )
(B+)
(A – )
FG
SG
RDB+
RDA–
SDB+
SDA–
(SG)
FG
SG
RDB+
RDA–
SDB+
SDA–
(SG)
(B+)
(A – )
Note
• The method used to eliminate noise varies depending on the situation. In the connection
example, the shield of the cable is connected only to the GX/GP’s ground (one-sided
grounding). This is effective when there is a difference in the electric potential between
the computer’s ground and the GX/GP’s ground. This may be the case for long distance
communications. If there is no difference in the electric potential between the computer’s ground
and the GX/GP’s ground, the method of connecting the shield also to the computer’s ground
may be effective (two-sided grounding). In addition, in some cases, using two-sided grounding
with a capacitor connected in series on one side is effective. Consider these possibilities to
eliminate noise.
• When using the two-wire interface (Modbus protocol), the 485 driver must be set to high
impedance within 3.5 characters after the last data byte is sent by the host computer.
1.2 Operations over the Serial Interface