INTRODUCTION
I-E96-624A
2 - 1
SECTION 2 - DESCRIPTION AND OPERATION
INTRODUCTION
This section explains the operation of the Plant Loop to Plant
Loop Remote Interface.
LOCAL/REMOTE COMMUNICATIONS
Local and remote PPTs communicate with each other through
a series of commands and replies over the serial ports. In the
one-way mode, the local PPT issues commands only; in
two-way, both the local and remote PPTs issue commands. The
command format is:
where:
1. Loop number is the loop that responds to the command (1
byte field).
2. Message byte count is the total length of the message (2
byte field).
3. Command code is the command code the PPT processes (1
byte field).
4. Command data is the specific command (variable length
field).
5. Checksum is the sum of all the bytes in the command (1
byte field) or CRC, the cyclic redundancy check word computed
for all of the bytes in the command using the CRC-16 algo-
rithm (2 byte field).
All communications between interfaces use this format.
INPPR01 commands are a modified form of Plant Loop to Com-
puter Interface commands (refer to I-E93-905-9 for command
details). The PPT format eliminates the key field from the PCI
command. In addition to PCI commands, the PPT processes a
command (code 29) that permits passage of a required PPT
message.
1
2
3
4
5
Loop
Number
Message
Byte Count
Command
Code
Command
Data
Checksum or
CRC
