Modem Modes of Operation
MC1321x Reference Manual, Rev. 1.6
7-12
Freescale Semiconductor
13. When a packet is successfully received, the following are reported:
a) crc_valid, IRQ_Status Register 24, Bit 0 - reports the results of the CRC check, where a “1”
indicates valid CRC. GPIO2 also reports valid CRC.
b) cca_final[7:0], RX_Pkt_Latch Register 2D, Bits 15 - 8 - reports Link Quality Indicator.
c) rx_done_irq, IRQ_Status Register 24, Bit 13 - reports the completion of packet reception,
where a “1” indicates 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 RX packet.
In between reading of the payload data, the MCU can be processing the data as it arrives. In this manner
once the frame has been validated, the MCU can respond with a reply (if required) with a minimum amount
of latency.
7.3.4.2
Aborting a Stream Receive Mode Sequence
It may be required to abort a stream receive sequence. The sequence should be aborted by negating
RXTXEN to low. The RX sequence will be terminated and the transceiver will return to the Idle condition.
The rx_done_irq status will be set and generate an interrupt (if enabled).
Because of the Streaming Data Mode, it is possible for a strm_data_err status/interrupt to occur up to 64
µsec after the transceiver returns to Idle. Driver software must deal with this extraneous interrupt by not
reacting to it other than to clear the status by reading the IRQ_Status Register 24. One means of detecting
that the interrupt is not valid is to monitor the Idle state of the transceiver through use of GPIO1 (out of
idle) indicator, such that if the interrupt occurs while the transceiver is in idle, then the interrupt status must
be cleared and ignored.
7.3.4.3
Stream Transmit Mode
The advantage of Stream Transmit Mode is that it allows the microcontroller to start a transmission without
the latency of pre-loading the TX data into the TX Packet RAM. The disadvantage of Stream Mode is that
there is a significant amount of overhead required from the MCU to process outgoing data on a
word-by-word basis.
NOTE
This following shows use of the RXTXEN signal to control a sequence. The
RXTXEN signal can be tied high and left high. The sequence will then start
based on writing of the bit tx_strm.
The following is a typical sequence for stream transmit operation not using a timer-based start (note that
xcvr_seq[1:0] field = 00):
1. The TX frequency must be programmed.
2. If not already low, the MCU sets RXTXEN low.
3. TX control bits must be programmed (Stream Mode and no timer):
a) tmr_trig_en = 0.
b) use_strm_mode = 1.
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