参数资料
型号: AT89LP51-20PU
厂商: Atmel
文件页数: 67/117页
文件大小: 0K
描述: MCU 8051 4K FLASH 20MHZ
标准包装: 10
系列: 89LP
核心处理器: 8051
芯体尺寸: 8-位
速度: 20MHz
连通性: EBI/EMI,I²C,SPI,UART/USART
外围设备: 欠压检测/复位,POR,PWM,WDT
输入/输出数: 36
程序存储器容量: 4KB(4K x 8)
程序存储器类型: 闪存
RAM 容量: 256 x 8
电压 - 电源 (Vcc/Vdd): 2.4 V ~ 5.5 V
振荡器型: 内部
工作温度: -40°C ~ 85°C
封装/外壳: 40-DIP(0.600",15.24mm)
包装: 管件
53
3709D–MICRO–12/11
AT89LP51/52
12.2
Capture 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 Figure 12-1.
The Timer 2 overflow rate in Capture mode is given by the following equation:
Figure 12-1. Timer 2 Diagram: Capture Mode
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. A summary of the Auto-Reload behaviors is listed in Table 12-5.
12.3.1
Up Counter
Figure 12-2 shows Timer 2 automatically counting up when DCEN = 0. 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 transition at external input
T2EX. This transition also sets the EXF2 bit. Both the TF2 and EXF2 bits can generate an inter-
rupt. The Timer 2 overflow rate for this mode is given in the following equation:
Capture Mode:
Time-out Period
65536
System Frequency
--------------------------------------------------
TPS
1
+
()
×
=
÷TPS
EXF2
T2EX PIN
T2 PIN
TR2
EXEN2
C/T2 = 0
C/T2 = 1
CAPTURE
OVERFLOW
TRANSITION
DETECTOR
TIMER 2
INTERRUPT
RCAP2H
RCAP2L
TL2
TH2
TF2
OSC
÷CDV
Table 12-5.
Summary of Auto-Reload Modes
DCEN
T2EX
Direction
Behavior
0
X
Up
reload to BOTTOM
1
0
Down
underflow to MAX
1
Up
overflow to BOTTOM
BOTTOM
MAX
MAX
BOTTOM
BOTTOM
MAX
Auto-Reload Mode:
DCEN = 0
Time-out Period
65536
RCAP2H RCAP2L
{,
}
System Frequency
-------------------------------------------------------------------------------
TPS
1
+
()
×
=
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