Horner APG XL4 OCS HE-ETN300 - Manual (Page 59)

SUP0740-07 CH.8
11/30/2009 Page 59 of 98 # 958
CHAPTER 8: MODBUS TCP SLAVE PROTOCOL
8.1 Modbus Overview
Modbus TCP is a Master / Slave protocol, which allows a remote Modbus TCP Master (client) to
request services from a Modbus TCP Slave (server). In this context, the Ethernet Module acts as
a Modbus TCP Slave, which responds to requests from one or more Modbus TCP Masters.
All Modbus requests that contain the Ethernet Module’s IP Address are serviced. The master
needs to be configured with the Ethernet Module’s IP Address, and most masters also require the
slave unit number. Since each Ethernet Module must have its own unique IP Address, the slave
unit number is not relevant and is discarded by the Ethernet Module.
To access OCS registers, a Modbus TCP Master must be configured with the appropriate register
type and offset. This is usually accomplished with one of two methods:
The first method uses either Traditional Modbus References or Expanded Modbus
References, in which the high digit represents the register type and the lower digits represent the
register offset (starting with register 1 for each type). Since only four Modbus register types (0, 1,
3 and 4) can be represented in this manner, the Ethernet Module’s Modbus implementation packs
several OCS register types into each Modbus register type. Starting addresses of each OCS
register type are shown in the Traditional Modbus Reference and Expanded Modbus
Reference columns of Table 8.1.
The second method requires the Modbus TCP Master to be configured with a specific Modbus
Command and Offset. The supported Modbus commands and the associated offsets are also
illustrated in Table 8.1.
Table 8.1 - Modbus Master Mapping
OCS
Reference
Maximum
Range
Traditional
Modbus
Reference
Expanded
Modbus
Reference
Modbus
Command(s)
Modbus
Offset
%Q1 2048 00001 000001 00000
%M1 2048 03001 003001 03000
%T1 2048 06001 006001 06000
%QG1 256 09001 009001
Read Coil Status (1)
Force Single Coil (5)
Force Multiple Coils (15)
09000
%I1 2048 10001 100001 00000
%IG1 256 13001 103001 03000
%S1 256 14001 104001 04000
%K1 256 15001 105001
Read Input Status (2)
05000
%AI1 512 30001 300001 00000
%AIG1 32 33001 303001 03000
%SR1 32 34001 304001
Read Input Register (4)
04000
%AQ1 512 40001 400001 00000
¾ %R1 2048 43001 403001 03000
%AQG1 32 46001 406001 06000
™ %R1 9999 - 410001
Read Holding Registers (3)
Preset Single Register (6)
Preset Multiple Registers (16)
10000
¾ All Ethernet modules support legacy register accessing (%R1-2048).
™ Only ETN300 modules support extended register accessing (%R1-9999).