User Manual
“Halo” System: Communication Protocol 970-00002-000
EXI Wireless Systems, Confidential Page 28 of 33 July 27, 1999
Lower 6 bits: message type
1 Network
Address
Logical address assigned by the Host
X Data Message contents. Number of bytes is variable, it could be 0.
1 Checksum All bytes added and inverted
Note: SOH character (01 Hex) defines start of the message and in a case that the same value (01 Hex) is
part of the rest of the message that byte is converted by using ESC character in the following
manner:
01 Hex (SOH) ⇒ 1B Hex 31 Hex (ESC ‘1’)
1B Hex (ESC) ⇒ 1B Hex 1B Hex (ESC ESC)
This conversion is done to avoid byte “01” Hex within the message to be considered as a start of the
new message.
The “Message Type” field is divided into two sub-fields, one is actual message type and the other (upper
two bits) is a counter (“message number”) which is advanced every time when the message is sent to the
particular RIM. Upon receiving the message from the host, the RIM advances its own message counter
which should be in sync with the received “message number”. If these two counters do not match, it
indicates to the RIM that it has missed at least one message from the Host.
7.5. Message Structure
All messages types are initiated by the Host, but not all of them are sent by the Host. Four message types
are sent by the Host, and the rest is sent by the RIMs as a response to Host’s messages. All message types
are listed in the Table 11
Table 11 Message Types
Asign
Network
Address
Test Node
Presence
Node
Present
Send /
Request
Data
Device
Data
Host Ack
Length 6 6 4 4 4 + (N * 4) 3
Type 2 3 4 5 6 7
Address Network
Address
00 00 or
Network
Address
Network
Address
Network
Address
Network
Address
Data Serial
Number
Serial
Number
Firmware
version #
Control
Byte
Status byte
7.5.1. Assign Network address
This message is sent by the Host when the network is configured. Part of network setup is to assign
network address to each device on the bus (each RIM). In order to do this, installer needs to know RIM’s ID
number (6 digit number). This message is then sent to that particular RIM which will use this number in all
future communication to the Host.