Specifications

Remote Diagnostics and Debugging

Debugging an Application Program 115

• <count> is the number of bytes that follow the command or

response packet. This lets the terminal know how long the packet

will be. The count includes the following:

Bytes

Item Counted

1 Count

1 Command

(variable) Number of bytes = length of data in bytes

1 1st CRC character

1 2nd CRC character

• <command> is a one-byte character identifying the command.

• The <data> portion of the packet contains the variable

information, if any, related to the diagnostic command.

• The two CRC characters (<CRC1> <CRC2>) represent the

standard CRC16 accumulation for the foregoing packet; they are

used for error detection.

Error Detection Protocols

If the terminal receives a packet with the wrong CRC, it sends a

packet containing the NAK (negative acknowledgment) back to the

diagnostic computer. This indicates to the diagnostic computer that it

has to re-send the packet to the terminal.

The diagnostic computer can also send an identical NAK packet to

the terminal. This tells the terminal to re-send the last packet and can

be used by the diagnostic computer whenever the terminal sends back

a packet containing the incorrect CRC.

The format for the NAK data packet is:

O3200 RM Book.book Page 115 Thursday, April 29, 1999 3:48 PM