Aquaread LeveLine, Instruction Manual

Page: 78 / 90

LeveLine ® Instruction Manual 10401-01026 Rev D
Table 3 summarises the Modbus functions supported by the LeveLine ® and the following
subsections describe their command & response packet formats.
Function Function Code
Read Holding Registers 0x03
Read Input Registers 0x04
Write Holding Register 0x06
Write Holding Registers 0x10
Report Slave ID 0x11
Table 3: Supported Modbus Functions
6.14.1. Exception Responses
If a command is unsupported or has invalid parameters, the LeveLine ® will return an
exception response with the format:
Field Size Content
<a> 1 byte Slave address
<exception-function-
code> 1 byte Function code of the c 0x80
<exception-code> 1 byte The type of exception
1 – Unsupported command function code
2 – Invalid data address in command
3 – Invalid data value in command
<crc> 2 bytes CRC
6.14.2. Read Holding Registers
This command reads one or more Modbus holding registers, and has the format:
Field Size Content
<a> 1 byte Slave address
<function-code> 1 byte 0x03
<start-address> 2 bytes Base address of the block of registers to be read
(0x0000-0xFFFF)
<nr-registers> 2 bytes The number of registers to be read (0x0001-
0x007D)
<crc> 2 bytes CRC
NOTE: The address in the <start-address> field is the register number – 1.
The LeveLine
®
will send a response with the format:
Field Size Content
<a> 1 byte Slave address
<function-code> 1 byte 0x03
<values-size> 1 byte Size in bytes of <values> field (equal to 2 x <nr-
registers>)
<values> <values-
size> bytes Block of data containing the values of the requested
registers, 2 bytes per register, registers in order of
increasing address from <start-address> onwards
<crc> 2 bytes CRC
© 2019 Aquaread ® Ltd. www.aquaread.com Page 78 of 90