No
. 96-1886-01E
Rev
.
1.1
GTECH Aircon Radio (Model GWT154)
PAGE
28
OF
72
5.4
Single
Unicast
MAC
Packet
GTECH485 packets less than the maximum 802.15.4 payload capacity are encapsulated in a single
MAC packet. The currently selected End Device address in the Access Control List is the packet’s
destination.
Figure 14 - Single MAC Packet Exchange
5.5
Fragmented
Packets
Host CPU packets greater than the maximum 802.15.4 payload capacity, it must be subdivided into
smaller fragments. Fragmentation may be performed by either the Host CPU or the Radio module.
The following fragmentation is for the proposed Radio module method.
Serial data from the Host CPU to the Coordinator radio is buffered until the entire packet (up to 544-
bytes) is received, before beginning the RF transfer. The radio does not begin the RF transfer as soon
after 80 (or more) bytes have been received via the serial port as this would add complexity to the
sequence if the transfer were to be truncated, or in error. By increasing the Host interface serial data
rate to 230.4Kbps results in the serial latency being a relatively small percentage of the over-all packet
transmission time.
The End Device radio reassembles fragments into a buffer until the entire packet has been received,
before sending it to the peripheral.
Fragments must be sent and received in sequence; a fragment received out of sequence implies a lost
