AvaLAN Wireless AW900mSPI-10 - Manual (Page 23)

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AW900mSPI User’s Manual
The XC1220’s receive FIFO does not have data protection. This means that when
data is received from the RF, the host microcontroller has up to 50ms to remove the
data from the FIFO before data corruption occurs.
The transmit FIFO does utilize data protection. If the host microcontroller attempts
to send data to the XC1220 while the transmit FIFO is full (indicated to the host
microcontroller using the FIFO_Full line) the data will be discarded. Please note
that in UART mode, there is no FIFO_Full line. Because the UART baud rate is much
slower than the radio’s transmit rate, transmit overflow should not occur.
Data from the AP can be sent to one specific SU or broadcast to all SUs. Broadcast
data has no retransmissions and is not guaranteed to reach all SUs. Data from an SU
is always sent to the AP with retransmissions. Data is divided up into blocks for RF
transmission. This division of the data allows for better interference immunity and
re-transmission performance.
The getPacket command is used to read received data from the XC1220. The Data
Ready line (pin 9) will be asserted when data is present in the receive FIFO and will
remain asserted until all data is read. Once the Data Ready line has been asserted
the host microcontroller has approximately 50ms until the data becomes corrupted
in a high traffic scenario. Obviously in UART mode, the host microcontroller must be
ready to receive data at any time.
getPacket SPI Mode: 0x0A UART Mode: N/A
b7 b6 b5 b4 b3 b2 b1 b0
Byte 1 - ID6 ID5 ID4 ID3 ID2 ID1 ID0
Byte 2 S7 S6 S5 S4 S3 S2 S1 S0
Byte 3 - - - - - S10 S9 S8
Byte 4 DATA7 DATA6 DATA5 DATA4 DATA3 DATA2 DATA1 DATA0
...
Byte 4 is repeated until all the data is received
ID0 to ID6 is the 7-bit integer Device ID of the Subscriber Unit the data was received
from (Access Point only, for a Subscriber Unit the data is undefined).
S0 to S10 is the 11-bit integer size of the Data packet in bytes (number of data bytes
to read).
The setPacket command is used to submit data to the transmit FIFO for RF trans-
mission. The FIFO Full line (Pin 10) will be asserted if the transmit FIFO cannot
accept any more data. If the host microcontroller attempts to submit data while
the FIFO Full line is asserted then the Error Flag will also become asserted and the
data being submitted will not be entered into the FIFO. In UART mode, the host