Micromod MOD: MODBUS RTU Communications Guide - Manual (Page 25)

MODBUS RTU
COMMUNICATIONS GUIDE
21
Table 12. MODBUS Reference Information for MOD30 ML and Modcell Communications
Code Function Action Data Types Max Points per
Command
Address
Range
From To
01 Read Coil Status Read one or more
consecutive points Discrete 99 00001-00499 CL DRWIN1-5
02 Read Input Status Read one or more
consecutive points Discrete 99 10001-10499 CL DROIN1-5
03 Read Holding
Registers Read one or more
consecutive registers All except ASCII and HEX -
One Register per Point 32 40001-40499 ML SRWIN1-5
Any - Uses as many
Registers as req'd for Data 125 41001-45999 CL MRWIN1-5
04 Read Input
Registers Read one or more
consecutive registers All except ASCII and HEX -
One Register per Point 32 30001-30499 ML SROIN1-5
Any - Uses as many
Registers as req'd for Data 125 31001-35999 CL MROIN1-5
05 Force Single Coil Write one point Discrete 1 00001-00499 CL DRWIN1-5
06 Preset Single
Register Write one register All except ASCII and HEX -
One Register per Point 1 40001-40499 ML SRWIN1-5
Any - Uses as many
Registers as req'd for Data 1 41001-45999 CL MRWIN1-5
08 Loopback Test Return of Query (00) For Diagnostic Use Only N/A N/A N/A N/A
15 Force Multiple
Coils Write one or more
consecutive points Discrete 16 00001-00499 CL DRWIN1-5
16 Preset Multiple
Registers Write one or more
consecutive registers All except ASCII and HEX -
One Register per Point 16 40001-40499 ML SRWIN1-5
Any - Uses as many
Registers as req'd for Data 16 41001-45999 CL MRWIN1-5
65 Extended Modbus Read and/or Write any
Data Type
Any - Data in buffer, rather
than Coils or Registers Note 6 n/a CL FGLISTIN
NOTES:
1. Placing discrete points into Holding or Input Registers uses an entire 16 bit register for one point. This
may be more efficient when only a small amount of discrete data is required, along with analog data. If a
significant number of discrete points are required, communications and memory efficiency would be
improved by placing them into the Coil or Input Status area. Another possibility would be to pack 16
discrete points into a count and store it in an Input or Holding Register. This would be dependent on the
host device's ability to accept the packed data format.
2. Date, Floating Point and mSec Time are converted to 16 bit integers when tied to an ML register.
3. It is recommended that no more than the number of points supported per command be put into each Slave
ML block. This will prevent the Master device from accessing more than the allowed number of points in a
single command. The instrument will not return any data if the maximum number of registers is exceeded
or an invalid register is included. Some HMI packages, such as Fix DMACS, allow poll records to be
broken into groups to avoid this problem.
4. When using Extended Modbus, group control loop data together in CL blocks for greatest efficiency.
5. Some peripheral equipment that is designed for Modbus communications may not support Extended
Modbus (function code 65).
6. The instrument's foreground can hold up to 2400 bytes of data. The number of points that can be handled
per command depends on the host software. Connecting the CL block to BGLISTIN may provide
increased performance with some host configurations. This is the case when using Database Caching
with PC-30 or Genesis for Windows. Without Database Caching enabled, a connection to FGLISTIN is
recommended.
7. Each Modbus List block can contain up to 99 points, and each type of connection provides inputs for five
lists. This is also true for Configured List blocks for Standard Modbus. When using Extended Modbus,
Configured List blocks may be nested, allowing more than 99 points to be connected to FGLISTIN or
BGLISTIN.