Parker 8903/RS, Техническое руководство

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14
8903/RS RS485 Communications Interface
Exceptions
The following Modbus exception codes may be transmitted by the 8903/RS option during an
error response:
Code Name Description
01 ILLEGAL FUNCTION -
The function code is recognised but the function is
not supported.
02
ILLEGAL DATA
ADDRESS
- Attempting to read or write to a fixed parameter
(PREF) that does not exist or a DSE register that
has not been allocated.
- Attempting to write to a read-only register.
- Attempting to read or write only half of a 32-bit
value.
03 ILLEGAL DATA VALUE
- Attempting to write to a fixed parameter (PREF)
with a value that is out of range.
Rules
The mapped data (DSE registers, fixed parameters and special registers) may be read or written
to using the following functions:
Function Description 32-bit data broadcast Max number of registers
03 Read Holding Registers 9 8 125
04 Read Input Registers
9 8
125
06 Write Single Register 8 9 1
16 Write Multiple Registers 9 9 123
Reading or writing to a block of registers is permitted. However, the following rules apply:
ƒ Reading a block of Modbus registers when some of the registers within the block are not
allocated is permitted as long as the first register within the block is allocated. Registers that
have not been allocated to a fixed parameter or a DSE register will return a value of 0.
ƒ Writing to a block of Modbus registers when some of the registers within the block are not
allocated or are read-only is permitted as long as the first register within the block is allocated
and is not read-only. In this case read-only registers will not be affected.
ƒ If a block of registers ends on a Modbus register that maps onto a 32-bit fixed parameter
(PREF) or a 32-bit DSE register, then both Modbus registers that make up the 32-bit value
must be read from or written to.
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