參數(shù)資料
型號: AT89C55WD-24JU
廠商: Atmel
文件頁數(shù): 26/34頁
文件大?。?/td> 0K
描述: IC 8051 MCU FLASH 20K 44PLCC
產(chǎn)品培訓(xùn)模塊: MCU Product Line Introduction
標(biāo)準(zhǔn)包裝: 27
系列: 89C
核心處理器: 8051
芯體尺寸: 8-位
速度: 24MHz
連通性: UART/USART
外圍設(shè)備: WDT
輸入/輸出數(shù): 32
程序存儲器容量: 20KB(20K x 8)
程序存儲器類型: 閃存
RAM 容量: 256 x 8
電壓 - 電源 (Vcc/Vdd): 4.5 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
PIC10F200/202/204/206
DS41239D-page 30
2007 Microchip Technology Inc.
FIGURE 6-3:
TIMER0 TIMING: INTERNAL CLOCK/PRESCALE 1:2
TABLE 6-1:
REGISTERS ASSOCIATED WITH TIMER0
6.1
Using Timer0 with an External
Clock (PIC10F200/202)
When an external clock input is used for Timer0, it must
meet certain requirements. The external clock require-
ment is due to internal phase clock (TOSC) synchroniza-
tion. Also, there is a delay in the actual incrementing of
Timer0 after synchronization.
6.1.1
EXTERNAL CLOCK
SYNCHRONIZATION
When no prescaler is used, the external clock input is
the same as the prescaler output. The synchronization
of T0CKI with the internal phase clocks is accom-
plished by sampling the prescaler output on the Q2 and
Q4 cycles of the internal phase clocks (Figure 6-4).
Therefore, it is necessary for T0CKI to be high for at
least 2 TOSC (and a small RC delay of 2 Tt0H) and low
for at least 2 TOSC (and a small RC delay of 2 Tt0H).
Refer to the electrical specification of the desired
device.
When a prescaler is used, the external clock input is
divided by the asynchronous ripple counter-type
prescaler, so that the prescaler output is symmetrical.
For the external clock to meet the sampling require-
ment, the ripple counter must be taken into account.
Therefore, it is necessary for T0CKI to have a period of
at least 4 TOSC (and a small RC delay of 4 Tt0H) divided
by the prescaler value. The only requirement on T0CKI
high and low time is that they do not violate the
minimum pulse width requirement of Tt0H. Refer to
parameters 40, 41 and 42 in the electrical specification
of the desired device.
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Value on
Power-On
Reset
Value on
All Other
Resets
01h
TMR0
Timer0 – 8-bit Real-Time Clock/Counter
xxxx xxxx
uuuu uuuu
N/A
OPTION
GPWU
GPPU
T0CS
T0SE
PSA
PS2
PS1
PS0
1111 1111
N/A
TRISGPIO(1)
I/O Control Register
---- 1111
Legend: Shaded cells not used by Timer0. – = unimplemented, x = unknown, u = unchanged.
Note 1:
The TRIS of the T0CKI pin is overridden when T0CS = 1.
PC – 1
Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
Instruction
Fetch
Timer0
PC
PC + 1
PC + 2
PC + 3
PC + 4
PC + 6
T0
T0 + 1
NT0
NT0 + 1
MOVWF TMR0 MOVF TMR0,W MOVF TMR0,W MOVF TMR0,W MOVF TMR0,W MOVF TMR0,W
Write TMR0
executed
Read TMR0
reads NT0
Read TMR0
reads NT0
Read TMR0
reads NT0
Read TMR0
reads NT0 + 1
Read TMR0
reads NT0 + 2
Instruction
Executed
PC + 5
PC
(Program
Counter)
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