AT89LP3240_14 Datasheet, PDF (63/200 Pages) ATMEL Corporation – Nonvolatile Program and Data Memory

AT89LP3240/6440
Figure 12-1. Timer 2 Diagram: Capture Mode
OSC
÷TPS
C/T2 = 0
T2 PIN
T2EX PIN
C/T2 = 1
TRANSITION
DETECTOR
TR2
CAPTURE
TL2
TH2
TF2
OVERFLOW
RCAP2L RCAP2H
EXF2
TIMER 2
INTERRUPT
EXEN2
12.3
Auto-Reload Mode
Timer 2 can be programmed to count up or down when configured in its 16-bit auto-reload
mode. This feature is invoked by the DCEN (Down Counter Enable) bit located in the SFR
T2MOD (see Table 12-4). Upon reset, the DCEN bit is set to 0 so that timer 2 will default to
count up. When DCEN is set, Timer 2 can count up or down, depending on the value of the
T2EX pin. The overflow and reload values depend on the Timer 2 Count Mode bits, T2CM_1-0 in
T2MOD. A summary of the Auto-Reload behaviors is listed in Table 12-5.
Table 12-5.
T2CM_1-0
00
00
00
01
01
01
10
11
Summary of Auto-Reload Modes
DCEN T2EX Direction
0
X
Up
1
0
Down
1
1
Up
0
X
Up
1
0
Down
1
1
Up
X
X
Up-Down
X
X
Up-Down
Behavior
BOTTOM →MAX reload to BOTTOM
MAX →BOTTOM underflow to MAX
BOTTOM →MAX overflow to BOTTOM
MIN →TOP reload to MIN
TOP →MIN underflow to TOP
MIN →TOP overflow to MIN
MIN →TOP →MIN and repeat
MIN →TOP →MIN and repeat
12.3.1
Up Counter
Figure 12-2 shows Timer 2 automatically counting up when DCEN = 0 and T2CM_1-0 = 00B. In
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:
Auto-Reload Mode:
DCEN = 0, T2CM = 00B
Time-out Period
=
6_----5_---5_----3_---6_{-----–----{---}R_----C_-----A_----P_----2_---H_-----,---R_----C_----A_----P_----2_----L_--}--
Oscillator Frequency
×
(TPS + 1)
Timer 2 may also be configured to count from MIN to TOP instead of BOTTOM to MAX by set-
ting T2CM_1-0 = 01B. In this mode Timer 2 counts up to TOP, the 16-bit value in RCAP2H and
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