PIC16F819-I/SO Microchip Technology Inc., PIC16F819-I/SO Datasheet - Page 55

• Manufacturer Part Number: PIC16F819-I/SO
• Description: 18 PIN, 3.5 KB FLASH, 256 RAM, 16 I/O
• Manufacturer: Microchip Technology Inc.

Specifications of PIC16F819-I/SO

• A/d Inputs: 5-Channel, 10-Bit
• Cpu Speed: 5 MIPS
• Eeprom Memory: 256 Bytes
• Input Output: 16
• Interface: I2C/SPI
• Memory Type: Flash
• Number Of Bits: 8
• Package Type: 18-pin SOIC
• Programmable Memory: 3.5K Bytes
• Ram Size: 256 Bytes
• Speed: 20 MHz
• Timers: 2-8-bit, 1-16-bit
• Voltage, Range: 2-5.5 V
• Lead Free Status / Rohs Status: RoHS Compliant part Electrostatic Device

6.0
The Timer0 module timer/counter has the following
features:
• 8-bit timer/counter
• Readable and writable
• 8-bit software programmable prescaler
• Internal or external clock select
• Interrupt-on-overflow from FFh to 00h
• Edge select for external clock
Additional information on the Timer0 module is
available in the “PICmicro
Reference Manual” (DS33023).
Figure 6-1 is a block diagram of the Timer0 module and
the prescaler shared with the WDT.
6.1
Timer0
OPTION_REG register (see Register 2-2). Timer mode
is selected by clearing bit T0CS (OPTION_REG<5>).
In Timer mode, the Timer0 module will increment every
instruction cycle (without prescaler). If the TMR0 regis-
ter is written, the increment is inhibited for the following
two instruction cycles. The user can work around this
by writing an adjusted value to the TMR0 register.
FIGURE 6-1:
 2004 Microchip Technology Inc.
RA4/AN4/T0CKI
Note: T0CS, T0SE, PSA, PS2:PS0 are (OPTION_REG<5:0>).
WDT Enable bit
CLKO (= F
WDT Timer
31.25 kHz
TIMER0 MODULE
Timer0 Operation
pin
operation
OSC
/4)
T0SE
BLOCK DIAGRAM OF THE TIMER0/WDT PRESCALER
is
0
1
®
controlled
PSA
Mid-Range MCU Family
M
U
X
0
1
T0CS
M
U
X
through
8-bit Prescaler
0
8-to-1 MUX
Time-out
8
MUX
WDT
the
PRESCALER
1
0
1
PSA
M
U
X
Counter mode is selected by setting bit T0CS
(OPTION_REG<5>). In Counter mode, Timer0 will
increment either on every rising or falling edge of pin
RA4/AN4/T0CKI. The incrementing edge is determined
by the Timer0 Source Edge Select bit, T0SE
(OPTION_REG<4>). Clearing bit T0SE selects the
rising edge. Restrictions on the external clock input are
discussed in detail in Section 6.3 “Using Timer0 with
an External Clock”.
The prescaler is mutually exclusively shared between
the Timer0 module and the Watchdog Timer. The
prescaler is not readable or writable. Section 6.4
“Prescaler” details the operation of the prescaler.
6.2
The TMR0 interrupt is generated when the TMR0
register overflows from FFh to 00h. This overflow sets
bit, TMR0IF (INTCON<2>). The interrupt can be
masked by clearing bit, TMR0IE (INTCON<5>). Bit
TMR0IF must be cleared in software by the Timer0
module Interrupt Service Routine before re-enabling
this interrupt. The TMR0 interrupt cannot awaken the
processor from Sleep since the timer is shut-off during
Sleep.
PSA
PS2:PS0
Cycles
Timer0 Interrupt
Sync
2
PIC16F818/819
TMR0 reg
Data Bus
8
Set Flag bit TMR0IF
DS39598E-page 53
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