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1-5
Table 1.5: Exception Response (Error Codes)
02
03
06
Illegal Data Address
Illegal Data Value
Busy, Rejected Packet
The Slave does not recognize the address in the data field of the
transmitted request packet.
The value referenced in the transmitted request packet is not supported
by the register on the EPM Slave.
The Slave is busy performing a long operation and can not receive the
request packet.
Illegal Function01
The Slave does not support the function code of the transmitted request
packet.
DescriptionNameError Code
FOR n=1 to # of bytes in packet
XOR nth data byte with the 16-bit register
FOR bits_shifted = 1 to 8
SHIFT 1 bit to the right
IF (bit shifted out EQUAL 1)
XOR generator polynomial with the 16-bit register and store result in
the 16-bit register
END IF
END FOR
END FOR
The resulting 16-bit register contains the CRC-16 checksum.
1.6:
Dead
Time
Q
An EPM Slave considers a transmission from a Master complete when it has received no data for a
period of 3.5 byte transmission times—approximately 7 ms at 4800 baud and 300 microseconds at
115200 baud. If the Master transmits any gaps between bytes that are longer than this time period,
the Slaves will perceive it as dead time.
Q
At the conclusion of the dead time, all unaddressed Slaves begin listening for a new packet from the
Master.
1.7:
Exception
Response
(Error
Codes)
Q
An EPM Slave will send its Master an Exception Response packet, if it has encountered an invalid
command or other problem while carrying out the Master’s instructions. The function code of the
response will have the most significant bit set. The Data field of the Exception Response contains
an Error Code specific to the type of problem.
Q
Table 1.5 below lists the different Error Codes supported by EPM devices.