Digitax 4GMCU, Техническое руководство, Страница: 56 / 64

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Pack Number
The field Packet number contains a sequential number of packets ranging from 1 to 7 wrapping back
to 1 after 7 past.
The pourpose is to give the receiver the possibility of rejecting packets already correctly.
It could happen that the packet has reached the receiver who sends the corresponding ACK, but this
ACK is disturbed and is not interpreted by the sender.
The sender, in case of not receiving the acknowledge, resends the same packet, till 3 times (see
Handshake).
At this point the receiver which has already in its memory the correct copy of such packet, must have
the possibility to detect that the incoming data are already been received and must be
ignored.Implementation
Implementation for 4GMCU A.I.T.P. processor
Special In/Out
Request Status: The MCU requests the status of the Special I/O.
Return Status: Is the MSG returned by the AITP as answer to the GP command.
The returned byte has the following format:
bit 0 IN 1
1 IN 2
2 IN 3
3 GSM RING
4 OUT 1
5 OUT 2
Set Out: The MCU forces the status of the OUT port.
The command is composed by two bytes, the first is the out mask (force only outs with
corresponding bit mask = 1), the second byte is the out value.
bit 4 OUT 1
5 OUT 2