NEC NDA-30115-001 manual Transmission Protocol, ‘1’ ‘!’ 05H

Property Management System - Communication Interface Architecture

The control codes used for the message texts are:

		Table 2-2 Control Codes
Control Code	Hexadecimal	Function
	Value
STX	02	Indicates the start of a block.
ETX	03	Indicates the end of a block.
EOT	04	Indicates the end of transmission of a block or release of the
		data link by the sender.
ENQ	05	Used to query other party for expected response.
ACK	06	Indicates the positive acknowledgment of an information block
		or start sequence.
NAK	15	Indicates the negative acknowledgment of an information
		block or start sequence.
DLE <	10, 3C	Indicates the receiver interrupting to ask for sending rights.
DLE :	10, 7C	Indicates the receiver interrupting to ask the sender to stop
		transmission and to release the data link.
DLE ?	10, 3F	Used as the negative acknowledgment of block and indicates
		that the receiver temporarily cannot receive data from the
		sender.

Transmission Protocol

Before a message can be sent, a start sequence (also called a selecting sequence) must be sent to urge the receiver to receive the data. Every transmission sequence will begin with the sender sending a start sequence.

The start sequence is a three byte sequence:

0 1 2

‘1’

‘!’ 05H

SA UA ENQ

Figure 2-1 Start Sequence

NDA-30115 Revision 1.0 Page 5