5.3 T-CPU board (05P0732)
5-19
5.3.4 Interface circuit
Table 5.3.7 lists the ports on the transceiver unit.
Table 5.3.7 Ports on transceiver unit
Port Name Signal Name I/F Type Dip switch Connection
TD1-A, TD1-B
CONTROLLER-1
RD1-A, RD1-B
RS-485 -
TD1-A, TD1-B
CONTROLLER-2
RD1-A, RD1-B
RS-485 -
SD
RD
RS-232C
S3-#1/2 OFF
S3-#3/4 ON
Case 1
TD (MIF-A, MIF-B) RS-422
RS-422
REMOTE
(MIF)
RD (MIF-R)
C.Loop
Selectable with S2-#3
ON: RS-422
OFF: C.Loop,
-S3-#1/2
ON
-S3-#3/4
OFF
Case2
TD (IEC-A, IEC-B) RS-422
RS-422
IEC
RD (IEC-R)
C.Loop
Selectable with S2-#1
OFF: C.Loop,
ON: RS-422
TD (DMC-A, DMC-B) RS-422
RS-422
RD (DMC-R)
C.Loop
Selectable with
S2-#2
OFF: C.Loop,
ON: RS-422
S6: all ON
S7: all OFF
DMC
TD (DMC-A, DMC-B) C.Loop
DMC
RD (DMC-R) C.Loop
S6: all OFF, S7: all ON IC-302-DSC
RS-422 S4: all OFF, S5: all ON IC-xxx
RCV BZ
BZ OUT,
BZ IN, BZ CTR
C.Loop S4: all ON, S5: all OFF IC-303-DSC
RS-232C
The RS-232C signals, asynchronous data are represented by voltage levels with respect
to a system common. The data is bi-polar: a +3 to +12 volt indicates an ON (space)
condition while a –3 V to –12 volt indicates an OFF (Mark) condition. The “dead area”
between +3 V and –3 V is designed to absorb line noise.
The 15 m limitation of cable length can be stretched to about 30 m for ordinary cable, if
well screened and grounded, and about 100 m if the cable is low capacitance as well.
RS-422
RS-422 is a balanced interface. A pair of wires is used to carry each signal. The data is
encoded and decoded as a differential voltage between sender and receiver. A typical
truth table for a balanced interface is as follows:
VA-VB < -0.2 V=0, VA-VB > +0.2 V=1
If lines A and B are close together, they will be affected almost identically by external
electromagnetic noise. If the lines are also twisted together, then neither line is
permanently closer to a noise source than the other. Hence the well known “twisted
pair” is extremely effective in eliminating noise from the signal. The output signal level
swings between 0 to +5 V. The RS-422 is designed for greater distance and higher baud
rates than RS-232C.
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