System Considerations
MC1321x Reference Manual, Rev. 1.6
3-26
Freescale Semiconductor
Doze - Allows use of the Event Timer when active. The Event Timer can be used to cause a timed exit
from Doze, and the CLKO output can be kept active in Doze to provide a clock to the MCU Doze uses
considerable more current than Off or Hibernate. RAM and register data are retained and digital I/O retain
their state.
Although Idle is not considered a low power state, it is listed in
Table 3-8 for comparison. It is also
important to remember that all active states of RX, TX and CCA must be initiated from the Idle condition.
3.12.2
Special Consideration Where Modem Doze Current Is Higher Than
Specified
The Doze current (no CLKO output active) is specified as 35 A (typical) on the data sheet with the programmed CLKO frequency
at a default of 32.786 kHz. The Doze current can be considerably higher for certain combinations of higher CLKO frequencies
and event timer prescale options. These combinations consist of:
1. CLKO frequency = 16 MHz with prescale select at 5, 6, or 7.
2. CLKO frequency = 8 MHz with prescale select at 6, or 7.
3. CLKO frequency = 4 MHz with prescale select at 7.
All other combinations have no problems. The higher current will not occur every time Doze is enabled. There is no potential harm
either to the transceiver or its operation, the Doze current is simply higher.
To work around this issue, there are three choices:
1. Accept higher current in Doze mode.
2. Do not use any of the described combinations in Doze mode.
3. If a higher CLKO frequency is desired when using CLKO as an MCU clock source, and the desired
prescale select can cause a problem, just before entering Doze mode, program the CLKO frequency
to a lower value. Next, use the desired prescale value while in Doze. Finally, after exiting Doze
mode, reprogram CLKO to the desired frequency before releasing the MCU clock to the CLKO
source
Table 3-8. MC1321x Modem Low Power States
Mode
Current
(typ @ 2.7V)
Advantages
Disadvantages
Comment
Off
0.2
μA
Lowest power (leakage only)
Digital outputs tristated.
All RAM/register data lost.
M_RST must remain asserted.
All IC functions off.
Hibernate 1.0
μA
RAM/register data retained.
Digital outputs retain their states.
ATTN or M_RST used to exit
state.
Doze1
1 CLKO frequency at default value of 37.786 kHz.
35
μA
(no CLKO)
Crystal reference oscillator is on and
CLKO can be enabled. Timed exit is
possible. RAM/register data retained.
Digital outputs retain their states.
Much higher current than
Hibernate or Off.
Can exit on ATTN or M_RST or
timed exit is option. CLKO can
be kept active as a clock source.
Idle
500
μA
Fast transition to RX, TX, CCA
Much higher current than
Doze or Hibernate
State from which all TX, RX or
CCA is initiated.