Red Lion PAXCDC1,2 (RS232/RS485) - Manual (Page 2)

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RS232 Communications
RS232 is intended to allow only two devices to communicate over distances up
to 50 feet. Data Terminal Equipment (DTE) transmits data on the Transmitted
Data (TXD) line and receives data on the Received Data (RXD) line. Data
Computer Equipment (DCE) receives data on the TXD line and transmits data on
the RXD line. The PAX emulates a DTE. If the other device connected to the
meter also emulates a DTE, the TXD and RXD lines must be interchanged for
communications to take place. This is known as a null modem connection. Most
printers emulate a DCE device while most computers emulate a DTE device.
Some devices cannot accept more than two or three characters in succession
without a pause in between. In these cases, the meter employs a busy function.
As the meter begins to transmit data, the RXD line (RS232) is monitored to
determine if the receiving device is “busy”. The receiving device asserts that it
is busy by setting the RXD line into a space condition (logic 0). The meter then
suspends transmission until the RXD line is released by the receiving device.
RS485 Communications
The RS485 communication standard allows the connection of up to 32
devices on a single pair of wires, distances up to 4,000 ft. and data rates as high
as 10M baud (the PAX is limited to 19.2k baud). The same pair of wires is used
to both transmit and receive data. An RS485 bus is therefore always half-duplex,
that is, data cannot be received and transmitted simultaneously.
WIRING CONNECTIONS
12
TXD
RXD
COMM.
PAX METER (DTE)
RECEIVING DEVICE
2
NC
RXD
TXD
3
3 2
7 5 5
DTE
3
2
DB9
13
14
15
DTE DCE
DB25 DB25
Terminal Block Connection Figure
3 5 4 2
PAX CONNECTOR
Not used Not used Not used B- A+ COMM
1
5
9
6
PIN 3 RXD
PIN 5 COMMON
FEMALE
PIN 2 TXD
Extended Comms Connection Figure
Extended Comms Connection Figure
12 12
B( - )
33K 33K
33K 33K
+5V +5V
Transmit Transmit
Enable Enable
PAX METER PAX METER RECEIVING DEVICE RECEIVING DEVICE
A(+) (+)
COMM. COMM. *
NC NC
* OPTIONAL OPTIONAL
13 13
14 14
15 15
Terminal Block Connection Figure
SPECIFICATIONS
PAXH Isolation For Both Cards:
Isolation To Sensor Common: 1400 Vrms for 1 min.
Working Voltage: 125 V
Isolation To User Input Common: 500 Vrms for 1 min.
Working Voltage: 50 V
RS485 Communication Card
Type: RS485 multi-point balanced interface
Isolation To Sensor & User Input Commons: 500 Vrms for 1 min.
Working Voltage: 50 V. Not Isolated from all other commons.
Baud Rate: 300 to 19.2k
Data Format: 7/8 bits; odd, even, or no parity
Bus Address: 0 to 99, max 32 meters per line
Transmit Delay: Selectable; 2 - 50 msec or 50 - 100 msec
RS232 Communication Card
Type: RS232 half duplex
Isolation To Sensor & User Input Commons: 500 Vrms for 1 min.
Working Voltage: 50 V. Not Isolated from all other commons.
Baud Rate: 300 to 19.2k
Data Format: 7/8 bits; odd, even or no parity