AT89LP828 Atmel Corporation, AT89LP828 Datasheet - Page 55

• Manufacturer Part Number: AT89LP828
• Manufacturer: Atmel Corporation

Specifications of AT89LP828

• Flash (kbytes): 8 Kbytes
• Max. Operating Frequency: 25 MHz
• Cpu: 8051-1C
• Max I/o Pins: 30
• Spi: 1
• Uart: 1
• Sram (kbytes): 0.75
• Eeprom (bytes): 1024
• Self Program Memory: IAP
• Operating Voltage (vcc): 2.4 to 5.5
• Timers: 3
• Isp: SPI/OCD
• Watchdog: Yes

12.2
12.3
3654A–MICRO–8/09
Capture Mode
Auto-Reload Mode
In the Capture mode, Timer 2 is a fixed 16-bit timer or counter that counts up from MIN to MAX.
An overflow from MAX to MIN sets bit TF2 in T2CON. If EXEN2 = 1, a 1-to-0 transition at exter-
nal input T2EX also causes the current value in TH2 and TL2 to be captured into RCAP2H and
RCAP2L, respectively. In addition, the transition at T2EX causes bit EXF2 in T2CON to be set.
The EXF2 and TF2 bits can generate an interrupt. Capture mode is illustrated in
The Timer 2 overflow rate in Capture mode is given by the following equation:
Figure 12-1. Timer 2 Diagram: Capture 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
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
T2MOD. A summary of the Auto-reload behaviors is listed in
Table 12-5.
T2EX PIN
T2CM
OSC
00
00
00
01
01
01
10
11
T2 PIN
1-0
Capture Mode:
Table
Summary of Auto-reload Modes
÷TPS
DCEN
TRANSITION
DETECTOR
12-4). Upon reset, the DCEN bit is set to 0 so that timer 2 will default to
X
X
0
1
1
0
1
1
C/T2 = 0
T2EX
C/T2 = 1
X
X
X
X
0
1
0
1
Time-out Period
EXEN2
Direction
Up-down
Up-down
Down
Down
Up
Up
Up
Up
TR2
CAPTURE
=
Behavior
BOTTOM
MAX
BOTTOM
MIN
TOP
MIN
------------------------------------------------------ -
Oscillator Frequency
MIN
MIN
→
→
→
→
→
→
RCAP2L
TOP
TOP
TOP
TOP
TL2
MIN
BOTTOM
65536
→
→
Table
EXF2
MAX
MAX
→
→
reload to MIN
underflow to TOP
overflow to MIN
RCAP2H
MIN
MIN
TH2
AT89LP428/828
12-5.
reload to BOTTOM
underflow to MAX
overflow to BOTTOM
and repeat
and repeat
OVERFLOW
×
(
TPS
TF2
+
1
Figure
)
INTERRUPT
TIMER 2
12-1.
1-0
55
in