Campbell Scientific CR10X Measurement and Control System - Manual (Page 278)

APPENDIX I. MODBUS ON THE CR10 AND CR10X
I-2
I.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 CR10 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 CR10.
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.
I.2.2 CR10 TO CR10 COMMUNICATION
Library special software is available that allows
one CR10X to communicate with another
CR10X using Modbus in a P97 instruction. The
standard implementation of Modbus enables
the CR10 to respond to Modbus commands, not
to issue them.
I.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 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 CR10 Description
1 read coil status
3 read holding registers
5 force single coil
15 force multiple coils
16 preset multiple registers
Example 1: Function 1 to read coils 1 to 16
from slave device 17
Hex
Slave address 11
Function 01
Starting Address Hi 00
Starting Address Lo 00
No. of Points Hi 00
No. of points Lo 16
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:
Binary
Hex 8765 4321
Slave address 11
Function 01
Byte Count 02
Data (Coils 7-0) CD 1100 1101
Data (Coils 15-8) 6B 0110 1011
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 CR10’s C1, C3, C4, C7, C8 are 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
Hex
Slave address x11
Function 03
Starting Address Hi 00
Starting Address Lo 09
No. of Points Hi 00
No. of points Lo 04
Error check (LRC or CRC) --