905U-G Wireless Gateway
User Manual
Page 93
©September 2004
The message interface supports the following types of communication:
• Command - Response
A message is sent by the message initiator, and the message recipient is required to
respond. The message initiator can be either the 905G or host device.
• Indication
A message is sent by the message initiator, and no response is required. The message
initiator can be either the 905G or host device.
Message Structure
A message consists of a message header and message data (see table below). The header
consists of a series of 16-bit registers that specifies the type of message and the length of the
message data. The message data may be up to 128 x 16bit registers in length and contain data
that is specific to the particular message.
Offset:
Register:
0
Message ID
1
Message Information
2
Command Number
3
Data Size
4
Extended Word 1
5
Extended Word 2
6
Extended Word 3
7
Extended Word 4
8
Extended Word 5
9
Extended Word 6
10
Extended Word 7
11
Extended Word 8
12
Message Data
:::
(up to
139
256 Bytes)
Message ID
The Message ID register contains a 16-bit integer identifier for the command. When a
response is sent back to the message initiator, the same message ID is used in that message.
Message ID’s can be selected arbitrarily, but successive messages must contain different ID’s
so as to trigger the execution of the message (i.e. a message will only be executed upon the
ID value changing).
Header
Data
