F.3 More On Modbus - Campbell CR510 Operator's Manual

APPENDIX F. MODBUS ON THE CR10(X) AND CR510
F.2.1 RF COMMUNICATIONS
The Campbell Scientific UHF/VHF radio
package is of course compatible with PC208.
To also do Modbus on SCADA packages using
the Campbell Scientific radio package, a special
operation system PROM for the RF95 radio
modem is needed. The RF95 PROMs will
facilitate an auto route to the correct RF95. The
RF95 address (dip switch) is set to the Modbus
address of the CR510 at each specific site in
this case. In the SCADA software the COM port
settings and the Modbus address need to be
set, but no dialing is necessary. The RF95s
would connect through to the correct CR510.
Repeater stations are not supported. ALL
REMOTES MUST COMMUNICATE DIRECTLY
TO THE RF232 BASE STATION.
Many of the popular radio systems for Modbus
applications are not compatible with PC208 if
there is more than one remote site.
F.2.2 CR510 TO CR510 OR CR10(X)
COMMUNICATION
Library special software is available that allows
one CR510 to communicate with another
CR510 using Modbus in a P97 instruction. The
standard implementation of Modbus enables
the CR510 to respond to Modbus commands,
not to issue them.

F.3 MORE ON MODBUS

Following is a brief explanation of the modbus
functions supported and the strings that are
transmitted. Most users will not need this
information as the CR10(X) and PC based
Modbus drivers handle this level of
communication transparent to the user. If more
information is needed, please refer to Modicon's
publication "Modicon Modbus Protocol
Reference Guide" (PI-MBUS-300 Rev. D). The
Modicon phone number is 508-794-0800.
Functions
supported
by CR510
1
3
5
15
16
F-2
Description
read coil status
read holding registers
force single coil
force multiple coils
preset multiple registers
Example 1: Function 1 to read coils 1 to 16
from slave device 17
Slave address
Function
Starting Address Hi
Starting Address Lo
No. of Points Hi
No. of points Lo
Error check (LRC or CRC) --
The coil status is returned as one coil per bit of
the data field. Coils 1 to 16 are addressed as 0
to 15. Response for example 1 follows:
Slave address
Function
Byte Count
Data (Coils 7-0)
Data (Coils 15-8)
Error check (LRC or CRC) --
The status of coils 7-0 is CD hex, or 1100 1101
binary. Coil 15 is the Most Significant Bit
(MSB). The CR510's C1 is on, C2, C5, and C6
are off. Flags 1,2,4,6, and 7 are high.
Example 2: Function 3 to read registers 40009
to 40012 from slave device 17 to retrieve input
locations 5 and 6 from the CR10(X)
Slave address
Function
Starting Address Hi
Starting Address Lo
No. of Points Hi
No. of points Lo
Error check (LRC or CRC) --
Hex
11
01
00
00
00
16
Binary
Hex 8765 4321
11
01
02
CD 1100 1101
6B 0110 1011
Hex
x11
03
00
09
00
04