PIC16F946T-I/PT Microchip Technology, PIC16F946T-I/PT Datasheet - Page 87

• Manufacturer Part Number: PIC16F946T-I/PT
• Description: Microcontroller
• Manufacturer: Microchip Technology
• Series: PIC® 16Fr

Specifications of PIC16F946T-I/PT

• Core Processor: PIC
• Core Size: 8-Bit
• Speed: 20MHz
• Connectivity: I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, LCD, POR, PWM, WDT
• Number Of I /o: 53
• Program Memory Size: 14KB (8K x 14)
• Program Memory Type: FLASH
• Eeprom Size: 256 x 8
• Ram Size: 336 x 8
• Voltage - Supply (vcc/vdd): 2 V ~ 5.5 V
• Data Converters: A/D 8x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 64-TFQFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: MA160011 - DAUGHTER BOARD PICDEM LCD 16F91X
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

5.4
An 8-bit counter is available as a prescaler for the
Timer0 module, or as a postscaler for the Watchdog
Timer. For simplicity, this counter will be referred to as
“prescaler” throughout this data sheet. The prescaler
assignment is controlled in software by the control bit
PSA (OPTION_REG<3>). Clearing the PSA bit will
assign the prescaler to Timer0. Prescale values are
selectable via the PS<2:0> bits (OPTION_REG<2:0>).
The prescaler is not readable or writable. When
assigned to the Timer0 module, all instructions writing
to the TMR0 register (e.g., CLRF 1,
BSF 1,
assigned to WDT, a CLRWDT instruction will clear the
prescaler along with the Watchdog Timer.
5.4.1
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 5-1 and
Example 5-2) must be executed when changing the
prescaler assignment from Timer0 to WDT.
TABLE 5-1:
© 2005 Microchip Technology Inc.
01h
0Bh/10Bh INTCON
81h
85h
Legend:
Address
Prescaler
– = Unimplemented locations, read as ‘0’, u = unchanged, x = unknown. Shaded cells are not used by the Timer0 module.
TMR0
OPTION_REG
TRISA
x....etc.) will clear the prescaler. When
SWITCHING PRESCALER
ASSIGNMENT
Name
REGISTERS ASSOCIATED WITH TIMER0
Timer0 Module register
TRISA7
RBPU
Bit 7
GIE
INTEDG
TRISA6
Bit 6
PEIE
TRISA5
T0CS
Bit 5
T0IE
MOVWF 1,
TRISA4
Preliminary
T0SE
INTE
Bit 4
TRISA3
RBIE
Bit 3
PSA
EXAMPLE 5-1:
To change prescaler from the WDT to the TMR0
module, use the sequence shown in Example 5-2. This
precaution must be taken even if the WDT is disabled.
EXAMPLE 5-2:
BCF
CLRWDT
CLRF
BSF
MOVLW
MOVWF
CLRWDT
MOVLW
MOVWF
BCF
CLRWDT
BSF
MOVLW
MOVWF
BCF
TRISA2
Bit 2
T0IF
PS2
STATUS,RP0
TMR0
STATUS,RP0
b’00101111’
OPTION_REG
b’00101xxx’
OPTION_REG
STATUS,RP0
STATUS,RP0
b’xxxx0xxx’
OPTION_REG
STATUS,RP0
TRISA1
Bit 1
INTF
PS1
TRISA0
CHANGING PRESCALER
(TIMER0
CHANGING PRESCALER
(WDT
RBIF
Bit 0
PS0
PIC16F946
;Bank 0
;Clear WDT
;Clear TMR0 and
; prescaler
;Bank 1
;Required if desired
; PS2:PS0 is
; 000 or 001
;
;Set postscaler to
; desired WDT rate
;Bank 0
;Clear WDT and
; prescaler
;Bank 1
;Select TMR0,
; prescale, and
; clock source
;
;Bank 0
xxxx xxxx uuuu uuuu
0000 000x 0000 000x
1111 1111 1111 1111
1111 1111 1111 1111
POR, BOR
Value on
TIMER0)
WDT)
DS41265A-page 85
Value on
all other
Resets