參數(shù)資料
型號: AT89S8253-24JI
廠商: Atmel
文件頁數(shù): 8/60頁
文件大?。?/td> 0K
描述: IC 8051 MCU FLASH 12K 44PLCC
標(biāo)準(zhǔn)包裝: 27
系列: 89S
核心處理器: 8051
芯體尺寸: 8-位
速度: 24MHz
連通性: SPI,UART/USART
外圍設(shè)備: POR,WDT
輸入/輸出數(shù): 32
程序存儲器容量: 12KB(12K x 8)
程序存儲器類型: 閃存
EEPROM 大?。?/td> 2K x 8
RAM 容量: 256 x 8
電壓 - 電源 (Vcc/Vdd): 2.7 V ~ 5.5 V
振蕩器型: 內(nèi)部
工作溫度: -40°C ~ 85°C
封裝/外殼: 44-LCC(J 形引線)
包裝: 管件
16
3286P–MICRO–3/10
AT89S8253
Figure 10-1. Timer 2 in Capture Mode
10.3
Auto-reload (Up or Down Counter)
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 10-3). 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.
Figure 10-2 shows Timer 2 automatically counting up when DCEN = 0. In this mode, two options
are selected by bit EXEN2 in T2CON. If EXEN2 = 0, Timer 2 counts up to 0FFFFH and then sets
the TF2 bit upon overflow. The overflow also causes the timer registers to be reloaded with the
16-bit value in RCAP2H and RCAP2L. The values in RCAP2H and RCAP2L are preset by soft-
ware. 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 interrupt if enabled.
Setting the DCEN bit enables Timer 2 to count up or down, as shown in Figure 10-3. In this
mode, the T2EX pin controls the direction of the count. A logic 1 at T2EX makes Timer 2 count
up. The timer will overflow at 0FFFFH and set the TF2 bit. This overflow also causes the 16-bit
OSC
EXF2
T2EX PIN
T2 PIN
TR2
EXEN2
C/T2 = 0
C/T2 = 1
CONTROL
CAPTURE
OVERFLOW
CONTROL
TRANSITION
DETECTOR
TIMER 2
INTERRUPT
÷12
RCAP2L
RCAP2H
TH2
TL2
TF2
Table 10-3.
T2MOD – Timer 2 Mode Control Register
T2MOD Address = 0C9H
Reset Value = XXXX XX00B
Not Bit Addressable
–––
––
T2OE
DCEN
Bit
765
43
210
Symbol
Function
Not implemented, reserved for future use.
T2OE
Timer 2 Output Enable bit.
DCEN
When set, this bit allows Timer 2 to be configured as an up/down counter.
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