72 SM-Applications Modules & Motion Processors User Guide
Issue Number: 4
Parameter data can be accessed in either 16-bit or 32-bit mode. The mode is selected
using the upper 2 bits of the register address, as follows:
Therefore, to access Pr
70.01 in 32-bit mode, the register number will be 40000 +
(0x4000 + 70×100 + 01) = 63385.
If a 32-bit parameter is read with 16-bit access mode, the least significant 16-bits will be
returned.
Note that the actual register number transmitted at the protocol level is one less than the
one asked for and does not include the 40000 offset. Most Modbus masters handle this
-1 difference automatically, but some don’t.
For master mode the following commands are used in the user DPL program:
• RtuReadHoldingRegs
• RtuReadHoldingParas
• RtuReadInputRegs
• RtuPresetMultipleRegs
• RtuPresetMutlipleParas
• RtuMasterReply
• RtuMasterStatus
6.1.2.1 FC03 Read multiple registers
Read a contiguous array of 16bit registers. The slave imposes an upper limit on the
number of registers which can be read. If this is exceeded the slave will issue an
exception code 2.
The following tables show the message constructs for Modbus RTU Function
Code 03.
Type field
bits 15-14
Access
00 16-bit. Backwards compatible
01 32-bit.
10 Reserved
11 Reserved
bit 15
TYP1
bit 14
TYP0
bits 13 - 0
Type select
Parameter address
x*100+Y-1
Table 6-5 Master request
Byte Description
0
Slave destination node address 1 through 247, 0 is
broadcast
1 Function code 0x03
2 Start register address MSB
3 Start register address LSB
4 Number of 16bit registers MSB
5 Number of 16bit registers LSB
6 CRC LSB
7 CRC MSB
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