PIC12F508_09 datasheet(38/110 Pages) MICROCHIP

38 / 110 page

PIC12F508/509/16F505

DS41236E-page 38

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 7.6 “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 program

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)

To change the prescaler from the WDT to the Timer0

module, use the sequence shown in Example 6-2. This

sequence must be used even if the WDT is disabled. A

CLRWDT

instruction

should

executed

before

switching the prescaler.

EXAMPLE 6-2:

CHANGING PRESCALER

(WDT

→ TIMER0)

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

CLRWDT

;Clear WDT and

;prescaler

MOVLW

‘xxxx0xxx’

;Select TMR0, new

;prescale value and

;clock source

OPTION

PIC12F508 Folha de dados(PDF) 38 Page - Microchip Technology

PIC12F508 Folha de dados(HTML) 38 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 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Folha de dados Download

Ligação URL