System Considerations
MC1321x Reference Manual, Rev. 1.6
Freescale Semiconductor
3-23
3.11
MC1321x Timer Resources
When writing software for the ZigBee specification and/or the 802.15.4 Standard applications, the user
should be aware of the set of timer resources available on the MC1321x. The timer resources derive from
both the MCU and modem functions and are individually best suited to different types of uses. The
functions include two MCU Timer/PWM (TPM) modules, the modem Event Timer block with four timer
compare registers, the MCU real time interrupt (RTI) for wake up from a low power mode, and the MCU
computer operating properly (COP) watchdog.
3.11.1
MCU TPM Modules
There are two MCU TPM modules that are primarily used to implement software timers and peripheral
timing based interfaces. The TPM module interface is memory mapped into the MCU address space and
has full separate interrupt capability. Each TPM has an independent 16-bit counter with prescaler and
modulo features to control frequency and range of a time reference The time base can be sourced from the
bus clock, fixed system clock, or an external pin.
The MCU has hardware to support a 3-channel TPM1 and a separate 5-channel TPM2. However, the
package limitations of the SiP allow only TPM1 Channel 2, and TPM2 Channels 1, 2, 3, and 4. TPM1
would be the first choice to implement a “time tick” for a software scheduler because of its limitation of
having only one I/O channel.
The input capture, output compare, and pulse width modulation (PWM) capabilities of the TPM allow for
a width range of control applications and peripheral functions. The TPM can be a useful interface into an
external sensor function.
The detailed description for the TPM is found in
Chapter 17, “MCU Timer/PWM (TPM Module)”
.
TX
1
0
1
0
TX
0
X
X
Hi-Z
Idle
1
X
X
0
Idle
0
X
X
Hi-Z
Doze
1
X
X
0
Doze
0
X
X
Hi-Z
Hibernate
1
X
X
0 (Low-Z)
Hibernate
0
X
X
Hi-Z
Off
X
X
X
Unknown
Table 3-7. CT_Bias Output vs. Register Settings (continued)
Mode
CT_Bias_en
RF_switch_mode
CT_Bias_inv
CT_Bias
Содержание freescale semiconductor MC13211
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Страница 166: ...Modem Modes of Operation MC1321x Reference Manual Rev 1 6 7 22 Freescale Semiconductor...
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