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180 HVAC Drive H300
Issue Number: 3
Reads when actual parameter type is different from selected
The slave will send the least significant word of a 32 bit parameter if that parameter is read as part of a 16 bit access.
The slave will sign extend the least significant word if a 16 bit parameter is accessed as a 32 bit parameter. The number of 16 bit registers must be
even during a 32 bit access.
Example, If Pr 01.028 is a 32 bit parameter with a value of 0x12345678, Pr 01.029 is a signed 16 bit parameter with a value of 0xABCD, and
Pr 01.030 is a signed 16 bit parameter with a value of 0x0123.
* Bit 14 is set to allow 32 bit access.
Writes when actual parameter type is different from selected
The slave will allow writing a 32 bit value to a 16 bit parameter as long as the 32 bit value is within the normal range of the 16 bit parameter.
The slave will allow a 16 bit write to a 32 bit parameter. The slave will sign extend the written value, therefore the effective range of this type of write
will be -32768 to +32767.
Examples, if Pr 01.028 has a range of ±100000, and Pr 01.029 has a range of ±10000.
* Bit 14 is set to allow 32 bit access
10.3.8 Exceptions
The slave will respond with an exception response if an error is detected in the master request. If a message is corrupted and the frame is not
received or the CRC fails then the slave will not issue an exception. In this case the master device will time out. If a write multiple (FC16 or FC23)
request exceeds the slave maximum buffer size then the slave will discard the message. No exception will be transmitted in this case and the master
will time out.
Exception message format
The slave exception message has the following format.
Exception codes
The following exception codes are supported.
Read
Start register
address
Number of 16 bit
registers
Response (Hex) Comments
Pr 01.028 127 1 0x5678
Standard 16 bit access to a 32 bit register
will return low 16 bit word of truncated data
Pr 01.028 16511* 2 0x12345678 Full 32 bit access
Pr 01.028 16511* 1 Exception 2
Number of words must be even for 32 bit
access
Pr 01.029 128 1 0xABCD
Standard 16 bit access to a 32 bit register
will return low 16 bit word of data
Pr 01.029 16512* 2 0xFFFFABCD
32 bit access to a 16 bit register will return
32 bit sign extended data
Pr 01.030 16513* 2 0x00000123
32 bit access to a 16 bit register will return
32 bit sign extended data
Pr 01.028 to
Pr 01.029
127 2 0x5678, 0xABCD
Standard 16 bit access to a 32 bit register
will return low 16 bit word of truncated data
Pr 01.028 to
Pr 01.029
16511* 4 0x12345678, 0xFFFFABCD Full 32 bit access
Write
Start register
address
Number of 16bit
registers
Data (Hex) Comments
Pr 01.028 127 1 0x1234
Standard 16 bit write to a 32bit register. Value
written = 0x00001234
Pr 01.028 127 1 0xABCD
Standard 16 bit write to a 32bit register. Value
written = 0xFFFFABCD
Pr 01.028 16511 2 0x00001234 Value written = 0x00001234
Pr 01.029 128 1 0x0123 Value written = 0x0123
Pr 01.029 16512 2 0x00000123 Value written = 0x00000123
Byte Description
0 Slave source node address
1 Original function code with bit 7 set
2 Exception code
3 CRC LSB
4 CRC MSB
Code Description
1 Function code not supported
2 Register address out of range, or request to read too many registers
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