PD6830X Explosion-Proof Modbus Scanners
Instruction Manual
8
Modbus Operating Modes
Master
Processes and displays data read from
Modbus RTU slave devices. Up to 16
process variables (PVs) from up to 16 slave
devices. Each PV programmed individually.
Slave
Processes data sent to it from a
Modbus RTU master device.
Note: Refer to Modbus Register Tables at
for details.
Snooper
Listens to the Modbus traffic and picks up a
specific register or registers being polled by
a Master device from a specific slave
device and processes the data being read.
Up to 16 process variables (PVs) from up to
16 devices.
If multiple registers are polled by the master
with one command, only the first returned
value will be read.
Master Poll
Time
0.1 to 99.9 sec. Time between read-
commands.
Master
Timeout
0.1 to 99.9 seconds. Time elapsed after a
poll request is made before the scanner
considers that request to have failed.
Number of
Retries
1-99. The number of retries the scanner will
make when requesting data before
reporting an error condition on the PV.
Snooper
Response
Time
0.1 to 99.9 seconds. Time since the last PV
update the before being considered an
error.
Slave Timeout
0.0 to 99.9 seconds. Time elapsed after the
last data received from a master before the
scanner considers the data to be out of
date. Programming 0 disables the timeout,
and PV data will be displayed indefinitely
despite not being updated regularly.
Serial Communications
Protocol
Modbus® RTU
Scanner Id
1 – 247. Specifies the address of the
PD6830X.
Baud Rate
1,200; 4,800; 9,600; 19,200; 38,400;
57,600; or 115,200 bps
Transmit Time
Delay
Programmable between 0 and 199 ms
Parity/Stop Bit
Even, odd, none with 1 stop bit, or none
with 2 stop bits
Byte-to-Byte
Timeout
Max of 1.5 character times or 750
μ
s
Note: Refer to Modbus Register Tables at www.predig.com for details.
Modbus Scanner Process
Variables
PV Inputs
Up to 16 independently programmed
Modbus process variables (PVs) may
be scanned (Master mode) or detected
(Snooper mode). Each of the 16
Modbus PVs may be enabled or
disabled.
Slave Id
Specifies which device on the bus to
monitor. Valid for Master and Snooper
modes only.
Assign the slave ID or address (1-247)
of each of the devices containing the
process variables to be displayed
(Slave ID for PV1-16).
Register Number
Specifies which register(s) to read in
the devices on the bus.
5 Digit Function 03: 40001–49999;
04: 30001–39999; or 65: 1–9999.
6 Digit Function 03: 400001–465535 or
04: 300001–365535; or 65: 1–65535.
Range is dependent on Function Code
selection (03, 04, or 65)
Will read 2 registers for Long integer
and Floating point data types; the
register entered and the next
consecutive register number.
Valid for Master and Snooper modes
only.
Function Code
03, 04, and 65 (used to read 32 bit
registers). Master & Snooper modes
only.
Data Type
Select the data format of the PVs.
Select between short integer (2 byte),
long integer (4 byte), or floating point
(4 byte). Slave mode uses floating point
only.
Byte Order
Integer data programmable as binary or
BCD, and signed or unsigned. Byte
order selectable as big-endian (1234),
little-endian (4321), byte swap big-
endian (2143), or byte swap little-endian
(3412). Byte swap unavailable for short.
