COP8AME9 Datasheet, PDF (30/83 Pages) National Semiconductor (TI) – 8-Bit CMOS Flash Microcontroller with 8k Memory, Dual Op Amps, Virtual EEROM, Temperature Sensor,10-Bit A/D and Brownout Reset

12.0 Timers
The device contains a very versatile set of timers (T0, T1, T2
and T3). Timers T1, T2 and T3 and associated autoreload/
capture registers power up containing random data.
12.1 TIMER T0 (IDLE TIMER)
The device supports applications that require maintaining
real time and low power with the IDLE mode. This IDLE
mode support is furnished by the IDLE Timer T0, which is a
16-bit timer. The user cannot read or write to the IDLE Timer
T0, which is a count down timer.
As described in Section 13.0 Power Saving Features, the
clock to the IDLE Timer depends on which mode the device
is in. If the device is in High Speed mode, the clock to the
IDLE Timer is the instruction cycle clock (one-fifth of the CKI
frequency). If the device is in Dual Clock mode or Low Speed
mode, the clock to the IDLE Timer is the 32 kHz clock. For
the remainder of this section, the term “selected clock” will
refer to the clock selected by the Power Save mode of the
device. During Dual Clock and Low Speed modes, the divide
by 10 that creates the instruction cycle clock is disabled, to
minimize power consumption.
In addition to its time base function, the Timer T0 supports
the following functions:
• Exit out of the Idle Mode (See Idle Mode description)
• WATCHDOG logic (See WATCHDOG description)
• Start up delay out of the HALT mode
• Start up delay from BOR
Figure 14 is a functional block diagram showing the structure
of the IDLE Timer and its associated interrupt logic.
Bits 11 through 15 of the ITMR register can be selected for
triggering the IDLE Timer interrupt. Each time the selected
bit underflows (every 4k, 8k, 16k, 32k or 64k selected
clocks), the IDLE Timer interrupt pending bit T0PND is set,
thus generating an interrupt (if enabled), and bit 6 of the Port
G data register is reset, thus causing an exit from the IDLE
mode if the device is in that mode.
In order for an interrupt to be generated, the IDLE Timer
interrupt enable bit T0EN must be set, and the GIE (Global
Interrupt Enable) bit must also be set. The T0PND flag and
T0EN bit are bits 5 and 4 of the ICNTRL register, respec-
tively. The interrupt can be used for any purpose. Typically, it
is used to perform a task upon exit from the IDLE mode. For
more information on the IDLE mode, refer to section Section
13.0 Power Saving Features.
The Idle Timer period is selected by bits 0–2 of the ITMR
register Bit 3 of the ITMR Register is reserved and should
not be used as a software flag. Bits 4 through 7 of the ITMR
Register are used by the dual clock and are described in
Section 13.0 Power Saving Features.
FIGURE 14. Functional Block Diagram for Idle Timer T0
20006318
TABLE 14. Idle Timer Window Length
ITSEL2 ITSEL1
0
0
0
0
0
1
0
1
ITSEL0
0
1
0
1
Idle Timer Period
High Speed
Mode
Dual Clock
or
Low Speed
Mode
4,096 inst.
cycles
0.125
seconds
8,192 inst. 0.25 seconds
cycles
16,384 inst. 0.5 seconds
cycles
32,768 inst.
cycles
1 second
ITSEL2 ITSEL1
1
0
1
0
1
1
1
1
ITSEL0
0
1
0
1
Idle Timer Period
High Speed
Mode
Dual Clock
or
Low Speed
Mode
65,536 inst.
cycles
2 seconds
Reserved - Undefined
Reserved - Undefined
Reserved - Undefined
The ITSEL bits of the ITMR register are cleared on Reset
and the Idle Timer period is reset to 4,096 instruction cycles.
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