19
®
Figure 1. LDM422 Logic Diagram
TD
RD
RTS
Echo Sup.
Echo Sup.
DTR
DSR
RLSD
CTS
+ 12VDC
Gnd
Case
RLSD
RD
DCE
DTE
TD
RTS
DTR
Light = High = Space
+V
CTS
* Light = High = Asserted
+V
+V
Light = Low = TD/RTS Enabled
Light = Low = Asserted
Light = Low = Space
+
-
+
-
B’
A’
RD
12VAC
PWR RTN
A’
B’
CTS
Opto-Iso
Barrier
+V
+V
+V
-12VDC
B
B
A
A
TD
RTS
SIG RTN
SIG RTN
(Isolated RS-422 Ground)
* "Light"is presence of light
across Opto-Iso barrier.
2
8
4
9
7
3
12
11
10
1
2
5
6
3
4
16
17
20
6
8
5
9
7
1
10
RS-232
P1
RS-422
P2
TD, RD
RTS, CTS, DTR, RLSD
Mark =-V; Space = +V
Asserted = + V, Not Asserted = -V
Mark
Space
Asserted
Not Asserted
Aor A’
Low
High
High
Low
BorB’
High
Low
Low
High
NOTE: Open or Tri-State on RD inputs produces
same logic condition as ’MARK’ input. Open or
Tri-State on CTS inputs produces same logic
condition as ’Asserted’ input.
TD, RD
RTS, CTS
RS-232 P1 P
RS-232 P1 P
RS-232 P1 P
RS-232 P1 P
RS-232 P1 Pin Descriptions
in Descriptions
in Descriptions
in Descriptions
in Descriptions
RS-422 P2 P
RS-422 P2 P
RS-422 P2 P
RS-422 P2 P
RS-422 P2 Pin Descriptions
in Descriptions
in Descriptions
in Descriptions
in Descriptions
Pin 1
Case
Case Ground
Pin 1
12VAC
Pin 2
TD
Transmit Data
Pin 2
PWR RTN
Pin 3
RD
Receive Data
Pin 3
RTS A
Pin 4
RTS
Request To Send
Pin 4
RTS B
Pin 5
CTS
Clear To Send
Pin 5
CTS A'
Pin 6
DSR
Data Set Ready
Pin 6
CTS B'
(connected to Data
Pin 7
TD A
Terminal Ready)
Pin 8
TD B
Pin 7
GND
Pin 9
SIG RTN
Pin 8
RLSD
Receive Line Signal Detect Pin 10
RD A'
Pin 9
+12VDC
Positive DC Supply Input
Pin 11
RD B'
Pin 10
–12VDC
Negative DC Supply Input
Pin 12
SIG RTN
Pin 16
Echo Sup Echo Suppression
(tie to pin 17 to enable)
Pin 17
Echo Sup Echo Suppression
(tie to pin 16 to enable)
Pin 20
DTR
Data Terminal Ready
(connected to Data
Set Ready)
The LDM422 conforms to EIA RS-232 and RS-422 specifications.
Data Terminal Ready must be asserted by the host RS-232 port before
the LDM422 can transmit data. When Data Terminal Ready is not
asserted all outputs of the LDM422 are high impedance, allowing up
to 32 LDM422 units to be multidropped on a common
communications cable. See Figures 1 and 3 for details.
Request To Send and Clear To Send are carried through the RS-422
port as two separate wire pairs. These may be used for full duplex
flow control.
Cable Capacitance Effects On Distances
Specified distances in the specifications are for the wire sizes 18-
24AWG (0.82-0.20mm2) with a maximum capacitance of 25pF/ft
(82pF/m). For higher capacitance cables, decrease distance