PIC10F200 datasheet(33/86 Pages) MICROCHIP

33 / 86 page

Preliminary

DS41239B-page 31

PIC10F200/202/204/206

6.1.2

TIMER0 INCREMENT DELAY

Since the prescaler output is synchronized with the

internal clocks, there is a small delay from the time the

external clock edge occurs to the time the Timer0

module is actually incremented. Figure 6-4 shows the

delay from the external clock edge to the timer

incrementing.

FIGURE 6-4:

TIMER0 TIMING WITH EXTERNAL CLOCK

6.2

Prescaler

An 8-bit counter is available as a prescaler for the

Timer0 module or as a postscaler for the Watchdog

Timer (WDT), respectively (see Section 9.6 “Watch-

dog Timer (WDT)”). For simplicity, this counter is

being referred to as “prescaler” throughout this data

sheet.

The PSA and PS<2:0> bits (OPTION<3:0>) determine

prescaler assignment and prescale ratio.

When assigned to the Timer0 module, all instructions

writing to the TMR0 register (e.g., CLRF 1, MOVWF 1,

BSF 1,x

, etc.) will clear the prescaler. When assigned

to WDT, a CLRWDT instruction will clear the prescaler

along with the WDT. The prescaler is neither readable

nor writable. On a Reset, the prescaler contains all ‘0’s.

6.2.1

SWITCHING PRESCALER

ASSIGNMENT

The prescaler assignment is fully under software

control (i.e., it can be changed “on-the-fly” during pro-

gram execution). To avoid an unintended device Reset,

the following instruction sequence (Example 6-1) must

be executed when changing the prescaler assignment

from Timer0 to the WDT.

EXAMPLE 6-1:

CHANGING PRESCALER

(TIMER0

→ WDT)

Increment Timer0 (Q4)

External Clock Input or

Q1 Q2

Q3 Q4

Q1 Q2

Q3 Q4

Q1 Q2

Q3 Q4

Q1 Q2

Q3 Q4

Timer0

T0 + 1

T0 + 2

Small pulse

misses sampling

External Clock/Prescaler

Output After Sampling

(3)

Prescaler Output (2)

(1)

Note 1:

Delay from clock input change to Timer0 increment is 3 TOSC to 7 TOSC (Duration of Q = TOSC). Therefore, the error

in measuring the interval between two edges on Timer0 input = ±4 TOSC max.

External clock if no prescaler selected; prescaler output otherwise.

The arrows indicate the points in time where sampling occurs.

Note:

The prescaler may be used by either the

Timer0 module or the WDT, but not both.

Thus, a prescaler assignment for the

Timer0 module means that there is no

prescaler for the WDT and vice versa.

CLRWDT

;Clear WDT

CLRF

TMR0

;Clear TMR0 & Prescaler

MOVLW

‘00xx1111’b ;These 3 lines (5, 6, 7)

OPTION

;are required only if

;desired

CLRWDT

;PS<2:0> are 000 or 001

MOVLW

‘00xx1xxx’b ;Set Postscaler to

OPTION

;desired WDT rate

PIC10F200 датащи(PDF) 33 Page - Microchip Technology

PIC10F200 датащи(HTML) 33 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86

датащи скачать

ссылки URL