No
. 96-1886-01E
Rev
.
1.1
GTECH Aircon Radio (Model GWT154)
PAGE
35
OF
72
Bits:
7 6 5 4 3 2 1 0
Field:
Fault
Reset
Busy
Req ?
Req 3
Req 2
Req 1
Req 0
Structure 4: GTECH Protocol Address Status
Refer to
[2]
for bit field assignments in Address Response Status byte.
A special Un-Listen address (0x16) in the restricted range may be issued by the Host CPU to force all
peripherals off-line. It is assumed the Un-Listen address does not receive an Address Response from
any peripheral.
The radio module should interpret Un-Listen as any address other than its own and forward it to the
End Device radios. Packets receive from the Host CPU, after the Un-Listen address has been issued,
should be discarded until another valid Peripheral address packet is received from the Host CPU and
acknowledged by an End Device.
The End Device radio will be required to act as a Terminal proxy whenever it receives a SYN address
packet from the Coordinator. The End Device radio outputs the SYN packet on its local wired 485
bus, and then triggers a response acceptance period timer. Typically, a two-byte packet should be
received by the End Device radio’s 485 bus with the first byte equaling the prior SYN packet’s address
value. A successful response message is encapsulated in an RF packet and returned to the Coordinator
radio. In the event of a timeout, or invalid response message, no RF response is issued. The Terminal
Host CPU is expected to provide its own failsafe timeout.
Bytes: 1
1
Fields: 0x16
SYN
0x16
Un-Listen
Structure 5: GTECH Un-Listen Address Packet
An optional Extended Address (0x1C) is defined by the GTECH485 protocol. This feature will not be
supported by the radio firmware at this time.
Bytes:
1 1 1
Fields: 0x16
SYN
0x1C
Extend
0x21 <= a <= 0xff
Extended Address (a)
Structure 6: GTECH Address Response Packet
7.1.4
GTECH
Data
Packet
The GTECH485 protocol does not employ a length parameter; detection of the reserved EOT (0x04)
byte denotes the end of a data packet. The peripheral may detect the EOT to determine when it has
received a complete message from the Host CPU, but will be required to implement a secondary
failsafe timeout in the event the termination character is missed or corrupted. An idle period of more
than 3.5 characters, since receiving the last character, will be inferred by the radio module to also
indicate termination of a Host packet.
The maximum payload length specified for a single GTECH485 Data Packet is 544 characters. This
does not include header bytes, but includes any exception character insertions that have taken place.
