Modem Modes of Operation
MC1321x Reference Manual, Rev. 1.6
Freescale Semiconductor
7-13
c) rx_strm = 0.
4. Program gpio_alt_en = 1 to enable GPIO1 as an “out-of_idle” indicator and GPIO2 as a CRC
“valid” indicator.
5. tx_sent_mask, Control_A Register 06, Bit 9 is programmed to “1” to enable an interrupt request
when a word of TX payload data needs to be written.
6. tx_done_mask, Control_B Register 07, Bit 7 is programmed to “1” to enable an interrupt request
when the TX packet has been fully sent.
7. The MCU loads the value of the number of data bytes plus two (for FCS) into tx_pkt_length[6:0]
TX_Pkt_Ctl Register 03, Bits 6 - 0.
8. The MCU preloads the first data word into TX_Pkt_RAM Register 02
9. tx_strm, Control_A Register 06, Bit 12 is programmed to “1” to enable the stream TX sequence.
10. RXTXEN must be asserted and held high.
11. The transmitter will turn-on, send preamble, the SFD, the FLI, and the first data word. When the
transceiver is ready to accept another data word, the tx_sent_irq, IRQ_Status Register 24, Bit 6,
will go valid and generate an interrupt request asking for the next word of payload data.
12. The microcontroller must respond to the interrupt by writing the TX data to tx_pkt_ram[15:0]
TX_Pkt_RAM Register 02.
NOTE
Steps 11 and 12 get repeated as required for the payload data. A word must
be transferred within 64 µs to keep the packet contiguous. No data transfer
is required for the FCS data because it is generated by the onboard
transceiver.
13. When the payload data packet has been successfully transmitted followed by the CRC bytes, the
MC1321x will generate a tx_done_irq, IRQ_Status Register 24, Bit 14 that reports the completion
of packet transmission, where a “1” indicate complete status. Also, an interrupt is generated due to
the valid status.
14. In response of the interrupt request from the MC1321x, the microcontroller checks status to clear
the interrupt and check the validity of the TX complete.
7.3.5
Clear Channel Assessment (CCA) Modes (including Link Quality
Indication)
A special case of receive function called Clear Channel Assessment (CCA) modes is available to measure
received energy from the selected channel. The CCA function exists as two algorithms:
1. Clear channel assessment - measuring channel energy and comparing to a preset threshold.
2. Energy detect (ED) - measuring channel energy and giving an indication of measured strength.
The energy detect algorithm is also used for Link Quality Indication (LQI) during a normal RX operation.
The LQI is reported as part of the RX operation.
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