Modem Modes of Operation
MC1321x Reference Manual, Rev. 1.6
7-6
Freescale Semiconductor
will not be cleared to an Idle value although the transceiver returns to the Idle condition. In this case, a read
from the xcvr_seq[1:0] field will return the code of the last programmed operation.
In Idle Mode, the crystal oscillator is active, CLKO is available (if enabled), and the SPI is active.
7.3.2
Controlling Transition to Other Active Modes from Idle
Reviewing the state diagrams in
signal RXTXEN must be asserted to allow transition from Idle to other active states. The recommended
procedure is that RXTXEN is taken low while setting-up the desired function (writing required registers)
and then after SPI transactions, the MCU raises RXTXEN to a high state enabling the transition. For timed
functions (using either tmr_cmp2 or tc2_prime), the same procedure holds with the exception that the
transition will be delayed until the timer function completes.
7.3.3
Packet Mode Data Transfer TX and RX Operation
Packet Mode assumes use of the onboard buffer RAMs and has the advantage of using less of the MCU
resources. The Idle Mode is the condition from which RX and TX modes are initiated. Writing to the
xcvr_seq[1:0] field arms the transition to the desired mode (use_strm_mode = 0, tx_strm = 0, and rx_strm
= 0). However, the RXTXEN signal must also be high for the transition to occur and if the Event Timer is
enabled, the transition will be synchronized to the timer compare event. Once Receive or Transmit is
entered, the MC1321x will transition back to the Idle Mode upon completion of the selected operation.
shows the transceiver sequence field modes.
The selected mode is controlled by:
1. xcvr_seq[1:0] field - Shown in
.
2. RXTXEN signal - The transition to any other active mode from Idle will not occur unless
RXTXEN is asserted high.
3. tmr_trig_en, Control_A Register 06, Bit 7 - When tmr_trig_en is set to “1”, the transition to the
selected active mode will be based on a tmr_cmp2[23:0] compare function as described in the
Event Timer section. When tmr_trig_en is cleared to “0”, the transition to the selected active mode
is based only on programming of xcvr_seq[1:0]. For both cases, RXTXEN must be high and
overrides.
4. For Packet Mode, tx_strm, rx_strm and use_strm_mode control bits must always be cleared to
zero.
Table 7-2. Transceiver Sequence Field (xcvr_seq[1:0])
Mode
Value
Description
Idle
00
Idle Mode - default state after exiting low-power modes
CCA / Energy Detect
01
CCA / Energy detect - special case of receive used to
monitor channel energy
Packet Receive
10
Packet Receive
Packet Transmit
11
Packet Transmit
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