PIC16F785-I/SO Microchip Technology, PIC16F785-I/SO Datasheet - Page 50

• Manufacturer Part Number: PIC16F785-I/SO
• Description: IC PIC MCU FLASH 2KX14 20SOIC
• Manufacturer: Microchip Technology
• Series: PIC® 16Fr

Specifications of PIC16F785-I/SO

• Program Memory Type: FLASH
• Program Memory Size: 3.5KB (2K x 14)
• Package / Case: 20-SOIC (7.5mm Width)
• Core Processor: PIC
• Core Size: 8-Bit
• Speed: 20MHz
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 17
• Eeprom Size: 256 x 8
• Ram Size: 128 x 8
• Voltage - Supply (vcc/vdd): 2 V ~ 5.5 V
• Data Converters: A/D 14x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Processor Series: PIC16F
• Core: PIC
• Data Bus Width: 8 bit
• Data Ram Size: 128 B
• Interface Type: RS- 232/USB
• Maximum Clock Frequency: 20 MHz
• Number Of Programmable I/os: 17
• Number Of Timers: 3
• Operating Supply Voltage: 2 V to 5.5 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• 3rd Party Development Tools: 52715-96, 52716-328, 52717-734
• Development Tools By Supplier: PG164130, DV164035, DV244005, DV164005, PG164120, ICE2000, DV164120, DM163029
• Minimum Operating Temperature: - 40 C
• On-chip Adc: 14-ch x 10-bit
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: XLT20SO1-1 - SOCKET TRANS ICE 20DIP TO 20SOICXLT18SO-1 - SOCKET TRANSITION 18SOIC 300MILAC162060 - HEADER INTRFC MPLAB ICD2 20PINAC164039 - MODULE SKT PROMATE II 20DIP/SOIC
• Connectivity: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

PIC16F785
5.3
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. Therefore, it is
necessary for T0CKI to be high for at least 2T
a small RC delay of 20 ns) and low for at least 2T
(and a small RC delay of 20 ns). Refer to the electrical
specification of the desired device.
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,x....etc.) will clear the prescaler. When
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,
TABLE 5-1:
DS41249A-page 48
01h,
101h
0Bh,
8Bh
81h,
181h
91h
85h,
185h
Legend:
Addr
TMR0
INTCON
OPTION_REG
ANSEL0
TRISA
Using Timer0 with an External
Clock
Prescaler
the
module.
SWITCHING PRESCALER
ASSIGNMENT
Name
— = Unimplemented locations, read as ‘0’, u = unchanged, x = unknown. Shaded cells are not used by the Timer0
following
REGISTERS ASSOCIATED WITH TIMER0
Timer0 Module register
RAPU
ANS7
Bit 7
GIE
—
instruction
INTEDG
ANS6
PEIE
Bit 6
—
TRISA5 TRISA4 TRISA3 TRISA2 TRISA1 TRISA0 --11 1111 --11 1111
T0CS
ANS5
Bit 5
T0IE
MOVWF 1,
sequence
OSC
(and
ANS4
T0SE
OSC
Bit 4
INTE
Preliminary
ANS3
RAIE
Bit 3
PSA
(Example 5-2 and Example 5-3) must be executed
when changing the prescaler assignment between
Timer0 and WDT.
EXAMPLE 5-2:
To change prescaler from the WDT to the TMR0
module, use the sequence shown in Example 5-3. This
precaution must be taken even if the WDT is disabled.
EXAMPLE 5-3:
BCF
BCF
CLRWDT
CLRF
BSF
MOVLW
MOVWF
CLRWDT
MOVLW
MOVWF
BCF
CLRWDT
BSF
BCF
MOVLW
MOVWF
BCF
ANS2
Bit 2
T0IF
PS2
STATUS,RP0
STATUS,RP1
TMR0
STATUS,RP0
b’00101111’
OPTION_REG
b’00101xxx’
OPTION_REG
STATUS,RP0
STATUS,RP0
STATUS,RP1
b’xxxx0xxx’
OPTION_REG
STATUS,RP0
ANS1
INTF
Bit 1
PS1
ANS0
Bit 0
RAIF
PS0
CHANGING PRESCALER
(TIMER0 WDT)
CHANGING PRESCALER
(WDT TIMER0)
 2004 Microchip Technology Inc.
;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 0000 0000 0000
1111 1111 1111 1111
1111 1111 1111 1111
POR, BOR
Value on:
Value on
all other
Resets