Specifications

Quintech Electronics and Communications Inc. Protocol Version 2.15 2

SRX Series Protocol

Protocol Message Structure

Commands packets can be sent over the Ethernet and serial ports (if available) and use a

standard STX/ETX protocol wrapper. Each packet includes a header byte, a two-byte address

field, a command byte, necessary data bytes, end byte, and a checksum byte. The bytes are

transmitted using an 8-bit word, with 1 stop bit and no parity. The general form for commands

and messages is:

Header Address Command Databyte(s) End Checksum

Control Bytes

Control bytes are transmitted as hexadecimal values.

Command Header Byte = STX (0x02)

Command End Byte = ETX (0x03)

Response Header Byte = ACK (0x06) for accepted commands.

Response Header Byte = NAK (0x15) for rejected commands.

Response End Byte = ETX (0x03)

The Header Byte (STX) is also used to reset the command receive buffer. If this byte is

received, it will be accepted as the beginning of a new message. The previous message will

be discarded. The only exception to this is if the byte (0x02) is a checksum byte. When the

buffer is reset, the checksum byte is also reset.

There is a 32-byte limit on command length. Any command longer than this will automatically

generate an error response if or when an ETX end byte is received. If a new STX is received

before an ETX, it will reset the command receive buffer and no error message will be sent.

If a break in communication occurs while a message is being transmitted (i.e., before the unit

receives the ETX and CHK byte), the buffer will clear and the command will be lost (no

response will be sent). This condition will occur if there is a delay of about 200 milliseconds

between bytes.

Address Field

The address field consists of two ASCII digits. The address for a control unit is normally set

using the front panel keypad. Each unit will only respond to a command with a matching

address. This allows multiple control units to be connected on a shared RS-422/485 control

bus. The address can be set from 00 to FF on units with front panel configuration.