Manual

2
SERIAL SET-UP DIP SWITCH OPERATION
Serial port configuration is accomplished through two banks of DIP switches
on the MODBUS card. The bank of 8 switches sets the Unit Address, the bank
of 7 switches sets the Serial port parameters (ASCII/RTU, 7/8 bits, Parity, and
Baud rate). Changes to the switch settings are only detected on power-up of the
unit. After changing a switch setting, power to the unit must be cycled for the
new switch setting to take effect.
Both unit address and serial set-up are set via DIP switches on the
MODBUS
option card. See the DIP switch setting table for more details on these
DIP switches.
For the Unit Address bank, the high order bit is switch 1, and the ON
position is a ‘1’, the OFF position is a ‘0’. Legal unit addresses are 1 to 247.
When a Unit Address of 0 is selected, the card responds to Unit Address 1.
When a Unit Address of 248 through 255 is selected, the card responds to Unit
Address 247.
For the serial bank, the following settings apply:
BAUD RATE SWITCH SELECTIONS
SWITCH SETTINGS AVAILABLE
RTU1 OFF: ASCII ON: RTU
8 Bits2 OFF: 7 Bits ON: 8 Bits
No Parity3 OFF: None ON: Parity
OFF4 OFF: Even ON: Odd
5 Baud Rate
9600
6 Baud Rate
(See Baud Rate
Switch Selections)
7 Baud Rate



5 6 7
38400:
ON ON ON
19200:
ON ON OFF
9600:
ON OFF ON
4800:
ON OFF OFF
2400:
OFF ON ON
1200:
OFF ON OFF
600:
OFF OFF ON
300:
OFF OFF OFF
SERIAL SET-UPUNIT ADDRESS
ON
12345678 1234567
BIT
WEIGHTS
(+128) (+64) (+32) (+16) (+8) (+4) (+2) (+1)
FACTORY
SETTINGS
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
3542
PAX CONNECTOR
Not used Not used Not used
B- A+
COMM
Extended Comms Connection Figure
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. RS485 is therefore always half-duplex, that
is, data cannot be received and transmitted simultaneously.