AR500 User’s Manual
LLL00xxxx – Rev 1.0
13
5.
Serial Interface Operation
This section refers to serial communication protocols for both the Sensor and
Module versions of the AR500.
5.1
Communications Protocol and Syntax
Serial port communication is required to configure the AR500 for operation.
The easiest way to communicate is by using a PC with an RS232
communication port and a terminal emulation program that uses hexadecimal
binary format. The factory default baud rate is 9600 bits/second.
Through these serial interfaces measurement data can be obtained by two
methods:
By single requests
Automatic streaming data
The serial data transmission byte has the following format:
1 start-bit
8 data bits
1 odd bit
1 stop-bit
The communications protocol is formed by communication sessions
(commands), which are only initiated by the ‘master’ (PC, controller). There
are two kinds of sessions with such structures:
1.
“request”, [“message”] — [“answer”],
square brackets include optional
elements
2.
“request” — “data stream” — [“request”].
5.1.1
Request
“Request” (INC) — is a two-byte message, which fully controls the
communication session. The ‘request’ message is the only one of all
messages in a session Where: the most significant bit is set at 0,
therefore, it serves to synchronize the beginning of the session. In
addition, it contains the device address (ADR), code of request (COD)
and optional message [MSG].
"Request" format:
Byte 0
Byte 1
[ Bytes
2…N ]
INC0(7:0)
INC1(7:0)
MSG
0 ADR(6:0)
1
0
0
0
COD(3:0)
5.1.2
Message
"Message’’ is data burst that can be transmitted by a ‘master’ in the
course of the session.
All messages with a "message" burst contain 1 in the most significant
digit. Data in a message are transferred in nibbles (aka:”tetrads”). When
a byte is transmitted, its lower tetrad goes first, and then follows the
