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The Hope transceiver module is what provides the Smart Packet Radio with its wireless capabilities. The microcontroller communicates with it using a SPI interface. The mode of operation used in the firmware provided is called FIFO mode. It operates by receiving the data intended for wireless transmission to be sent from the microcontroller and storing it in a FIFO buffer located on the transceiver module. Once the full packet has been stored in the buffer and the transceiver has been notified of the packet length, the microcontroller puts the transceiver into transmit mode. Once in transmit mode, the transceiver uses its internal packet handler to format the packet (the firmware formats it as shown in Figure 1) using the data in the FIFO as the payload.

f1-1.png Figure - Packet Format

The preamble length is configurable though in testing it was found that with a preamble of less than 2 bytes, the device would regularly receive a valid preamble erroneously. In FIFO mode the transceiver must have a sync word of at least one byte in length, so in testing the minimum was used. The destination address can either be specified to a board or can be set to 0xFF which means the broadcast is read by all devices. The source address of a board is coded in the firmware and can be easily altered.

-- XiaohongWu - 2012-01-30

Topic revision: r2 - 2012-01-31 - XiaohongWu
 
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