Modem Modes of Operation
MC1321x Reference Manual, Rev. 1.6
7-8
Freescale Semiconductor
4. rx_rcvd_mask, Control_A Register 06, Bit 8 is programmed to “1” to enable an interrupt request
when the RX packet has been received.
5. Transceiver sequence is programmed to xcvr_seq[1:0] = 0x2 for receive.
6. RXTXEN must be asserted and held high.
7. When a packet is successfully received, the following are reported:
a) rx_pkt_latch[6:0], RX_Pkt_Latch Register 2D, Bits 6 - 0 - reports the length of the packet
payload including 2 bytes of CRC data.
b) crc_valid, IRQ_Status Register 24, Bit 0 - reports the results of the CRC check, where a “1”
indicates valid CRC.
c) cca_final[7:0], RX_Pkt_Latch Register 2D, Bits 15 - 8 - reports Link Quality Indicator.
d) rx_rcvd_irq, IRQ_Status Register 24, Bit 7- reports the completion of packet reception, where
a “1” indicate complete status. Also, an interrupt is generated due to the valid status.
8. In response of the interrupt request from the MC1321x, the microcontroller does the following:
a) Determines the validity of the frame by reading and checking rx_rcvd_irq and crc_valid.
Determines a valid length for the frame by reading rx_pkt_latch[6:0].
b) Reads the payload data from RX Packet RAM using a recursive read from rx_pkt_ram[15:0]
RX_Pkt_RAM Register 01.
7.3.3.2
Aborting a Packet Receive Sequence
It may be required to abort a packet receive sequence. The RX sequence can be aborted by either negating
RXTXEN to low or by writing xcvr_seq[1:0] to 0x0. If either of these conditions happen, the transceiver
returns to Idle Mode and no additional status bit is set.
7.3.3.3
Packet Transmit Mode
The advantage of Packet Transmit Mode is that it allows the MC1321x to send the whole packet without
intervention from the microcontroller. The entire packet payload is pre-loaded in TX Packet RAM, the
MC1321x sends the frame, and then the transmit complete status is given to the MCU.
NOTE
This sequence shows use of the TXTXEN 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 field xcvr_seq[1:0].
The following is a typical sequence for packet transmit operation (not using a timer-based start):
1. The TX frequency must be programmed.
2. If not already low, the MCU sets RXTXEN low.
3. Control bits cleared (no Stream Mode and no timer):
a) tmr_trig_en = 0.
b) tx_strm = 0.
c) rx_strm = 0.
d) use_strm_mode = 0.
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