The TLP protocol

TLP224(R) is a registered trademark of Bull Corporation

The TLP protocol (Transport Layer Protocol) processing consists of two
steps. The first step is to construct the message to be transmitted.
Under the TLP224 protocol the GCR500 and the host system exchange
transmissions in the following format:

For messages transmitted without error:

<ACK><LN><MESSAGE><LRC>

where:

• ACK 60h, indicating that the previous command or status code was
  transmitted without error.

• LN Length of the message (command or status code)

• MESSAGE Command or status code.

• LRC The result of an EXCLUSIVE OR (XOR) between the characters ACK, LN, and MESSAGE.

When an error is detected in the transmission:

<NACK><LN><LRC>

where:

• NACK E0h, indicating that there was an error in a message transmission.

• LN 00

• LRC E0

During the second step the source performs the following processing:

• Adds an End Of Transmission (EOT) byte to the end of the transmission.
  This is the value 03h.

• Converts each byte to be transmitted into two ASCII characters. For example, to transmit the byte 3Ah, the source would transmit the values 33h and 41h. This prevents other equipment from interpreting the control characters.

For example, to transmit the power down command under the TLP224 protocol, which has the command code 4Dh and no parameter, the following sequence would be transmitted:

The timeout between each character is 100 ms.