Motorola M12 Oncore User's Guide download pdf (Page 34)

Chapter 3 – Receiver Description

Motorola GPS Products - Oncore User’s Guide

Motorola Binary Format

The binary data messages used by the Oncore Receiver consist of a variable number

of binary characters. These binary messages begin with the ASCII @@ characters

and are terminated with the ASCII carriage return and line feed <CR><LF>. The first

two bytes after the @@ characters are two ASCII characters that identify the

particular structure and format of the remaining binary data. The byte preceding the

termination <CR><LF> of all messages is a single byte checksum (the exclusive-or of

all message bytes after the @@ and before the checksum). Every message has the

following components:

Message Start:

@@ - (two hex 40s) denotes start of binary message.

Message ID:

(A.Z(a..z, A..Z) - ASCII upper-case letter, followed by an ASCII lowercase or

upper case letter. These two characters together identify the message type

and imply the correct message length and format.

Binary Data Sequence:

Variable number of bytes of binary data dependent on the command type.

Checksum:

C - The exclusive-or of all bytes after the @@ and prior to the checksum.

Message Terminator:

<CR><LF> - carriage return and line feed denoting the end of the binary

message.

Every Oncore receiver input command has a corresponding response message so

that you can determine whether the input commands have been accepted or rejected

by the Oncore receiver. The message format descriptions in Chapter 6 detail the input

command and response message formats. Information contained in the data fields is

normally numeric. The interface design assumes that the operator display is under

the control of an external system data processor and that display format and text

messages reside in its memory. This approach gives you complete control of the

display format and language.

The Oncore receiver reads the input command string on the input buffer once per

second. If a full command has been received, then it operates on that command and

performs the indicated function. Input character string checks are performed on the

input commands. A binary message is considered to be received if

it began with @@ and is terminated with a carriage return and a line feed,

the message is the correct length for its type, and

the checksum validates.

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Motorola M12 Oncore User's Guide Page 34