AT89LP428-20MU ATMEL [ATMEL Corporation], AT89LP428-20MU Datasheet - Page 56

• Manufacturer Part Number: AT89LP428-20MU
• Description: 8-bit Microcontroller with 4K/8K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

12.3.1
56
AT89LP428/828
Up Counter
Figure 12-2
this mode Timer 2 counts up to MAX and then sets the TF2 bit upon overflow. The overflow also
causes the timer registers to be reloaded with BOTTOM, the 16-bit value in RCAP2H and
RCAP2L. If EXEN2 = 1, a 16-bit reload can be triggered either by an overflow or by a 1-to-0 tran-
sition at external input T2EX. This transition also sets the EXF2 bit. Both the TF2 and EXF2 bits
can generate an interrupt. The Timer 2 overflow rate for this mode is given in the following
equation:
Timer 2 may also be configured to count from MIN to TOP instead of BOTTOM to MAX by set-
ting T2CM
RCAP2L and then overflows. The overflow sets TF2 and causes the timer registers to be
reloaded with MIN. If EXEN2 = 1, a 1-to-0 transition on T2EX will clear the timer and set EXF2.
The Timer 2 overflow rate for this mode is given in the following equation:
Timer 2 Count Mode 1 is provided to support variable precision asymmetrical PWM in the CCA.
The value of TOP stored in RCAP2H and RCAP2L is double-buffered such that a new TOP
value takes affect only after an overflow. The behavior of Count Mode 0 versus Count Mode 1 is
shown in
Figure 12-2. Timer 2 Diagram: Auto-reload Mode (DCEN = 0)
DCEN = 0, T2CM = 00B
DCEN = 0, T2CM = 01B
Auto-Reload Mode:
Auto-Reload Mode:
Figure
1-0
shows Timer 2 automatically counting up when DCEN = 0 and T2CM
= 01B. In this mode Timer 2 counts up to TOP, the 16-bit value in RCAP2H and
12-3.
÷TPS
Transition
Detector
Time-out Period
Time-out Period
Reload
=
=
65536
------------------------------------------------------------------------------ -
{
----------------------------------------------------------------- -
RCAP2H RCAP2L
Oscillator Frequency
Oscillator Frequency
TL2
–
{
RCAP2H RCAP2L
,
TH2
,
}
Overflow
+
1
×
(
}
TPS
3654A–MICRO–8/09
×
1-0
(
TPS
+
= 00B. In
1
Interrupt
Timer 2
)
+
1
)