GE EPM 9650/9800 manual Dead Time, Exception Response Error Codes

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

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.

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)

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.

Table 1.5 below lists the different Error Codes supported by EPM devices.

Table 1.5: Exception Response (Error Codes)

Error Code Name Description

01

02

03

06

Illegal Function

Illegal Data Address

Illegal Data Value

Busy, Rejected Packet

The Slave does not support the function code of the transmitted request 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.

1-5