User`s manual

Packet format: nn | nn | nnnn… | nnnn

address

command

registers and/or data

CRC

Watlow Controls Communications Guide 14

Packet Syntax

Each message packet begins with a one-byte controller address, from 0x01 to 0xF7.

The second byte in the message packet identifies the message command: read

(0x03 or 0x04); write (0x06 or 0x10); or loop back (0x08).

The next n bytes of the message packet contain register addresses and/or data.

The last two bytes in the message packet contain a two-byte Cyclical Redundancy

Checksum (CRC) for error detection.

Read Multiple Registers Command (0x03 or 0x04)

This command returns from 1 to 32 registers.

Packet sent to controller:| nn | 03 | nn nn | 00 nn | nn nn |

controller address (one byte)

read command (0x03 or 0x04)

starting register high byte

starting register low byte

number of registers high byte (0x00)

number of registers low byte

CRC low byte

CRC high byte

Packet returned by controller: | nn | 03 | nn | nn nn … nn nn | nn nn |

controller address (one byte)

read command (0x03 or 0x04)

number of bytes (one byte)

first register data low byte

first register data high byte

…

CRC low byte

CRC high byte