MDS 05-7280A01, Rev. A
MDS TransNEXT Technical Manual
17
Table 2-3. COM1 Port Pin Details (RS-485)
Pin
Number
Input/Output
Pin Description
1
OUT
ALARM Output
2
OUT
DCD (Data Carrier Detect)
3
Reserved
--
4
Ground
Connects to ground (negative supply potential) on chassis
5
OUT
TXD+/TXB (Transmitted Data +)
—Non-inverting driver output. Supplies
received payload data to the connected device.
6
IN
RXD+/RXB (Received Data +)
— Non-inverting receiver input. Accepts
payload data from the connected device.
7
OUT
TXD-/TXA (Transmitted Data -)
—Inverting driver output. Supplies
received payload data to the connected device.
8
IN
RXD-/RXA (Received Data -)
— Inverting receiver input. Accepts
payload data from the connected device.
COM1 Port notes and wiring arrangements (for RS-485)
•
The COM1 port supports 4-wire and 2-wire RS-485 mode as follows:
-
RXD+ / RXB and RXD– / RXA are data sent
into
the unit
-
RXD+ / RXB is positive with respect to RXD– / RXA when the line input is a “0”
-
TXD+ / TXB and TXD– / TXA are data sent
out
by the unit
-
TXD+ / TXB is positive with respect to the TXD– / TXA when the line output is a “0”
•
2-wire RS-485 mode connections:
-
Connect pins 5&6 (TXD+/RXD+) together and connect to (TXD+/RXD+) tied together on
connected device
-
Connect pins 7&8 (RXD-/TXD-) together and connect to (TXD-/RXD-) tied together on
connected device
•
4-wire RS-485 mode connections:
-
Connect pin 5 (TXD+) to RXD+ of connected device
-
Connect pin 6 (RXD+) to TXD+ of connected device
-
Connect pin 7 (TXD-) to RXD- of connected device
-
Connect pin 8 (RXD-) to TXD- of connected device
Figure 2-5 illustrates the 2-wire and 4-wire connections described above.
Figure 2-5. EIA-485 4-Wire/2-Wire Connections
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