PIC18F45K20-E/MV Microchip Technology, PIC18F45K20-E/MV Datasheet - Page 164
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PIC18F45K20-E/MV
Manufacturer Part Number
PIC18F45K20-E/MV
Description
32KB, Flash, 1536bytes-RAM, 36I/O, 8-bit Family,nanowatt XLP 40 UQFN 5x5x0.5mm T
Manufacturer
Microchip Technology
Series
PIC® XLP™ 18Fr
Datasheet
1.PIC18F25K20T-ISS.pdf
(456 pages)
Specifications of PIC18F45K20-E/MV
Processor Series
PIC18
Core
PIC18F
Data Bus Width
8 bit
Program Memory Type
Flash
Program Memory Size
8 KB
Data Ram Size
512 B
Interface Type
I2C, SPI, SCI, USB, MSSP, RJ11
Maximum Clock Frequency
64 MHz
Number Of Programmable I/os
35
Number Of Timers
4
Operating Supply Voltage
1.8 V to 3.6 V
Maximum Operating Temperature
+ 125 C
Mounting Style
SMD/SMT
Package / Case
UQFN-40
Development Tools By Supplier
MPLAB Integrated Development Environment
Minimum Operating Temperature
- 40 C
Operating Temperature Range
- 40 C to + 125 C
Supply Current (max)
30 uA
Core Processor
PIC
Core Size
8-Bit
Speed
48MHz
Connectivity
I²C, SPI, UART/USART
Peripherals
Brown-out Detect/Reset, HLVD, POR, PWM, WDT
Number Of I /o
35
Eeprom Size
256 x 8
Ram Size
1.5K x 8
Voltage - Supply (vcc/vdd)
1.8 V ~ 3.6 V
Data Converters
A/D 14x10b
Oscillator Type
Internal
Operating Temperature
-40°C ~ 125°C
Lead Free Status / Rohs Status
Details
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PIC18F2XK20/4XK20
13.9
Adding an external LP oscillator to Timer1 (such as the
one described in Section 13.6 “Timer1 Oscillator”
above) gives users the option to include RTC function-
ality to their applications. This is accomplished with an
inexpensive watch crystal to provide an accurate time
base and several lines of application code to calculate
the time. When operating in Sleep mode and using a
battery or supercapacitor as a power source, it can
completely eliminate the need for a separate RTC
device and battery backup.
The application code routine, RTCisr, shown in
Example 13-1, demonstrates a simple method to
increment a counter at one-second intervals using an
Interrupt Service Routine. Incrementing the TMR1
register pair to overflow triggers the interrupt and calls
the routine, which increments the seconds counter by
one; additional counters for minutes and hours are
incremented on overflows of the less significant
counters.
EXAMPLE 13-1:
DS41303G-page 164
RTCinit
RTCisr
Using Timer1 as a Real-Time Clock
MOVLW
MOVWF
CLRF
MOVLW
MOVWF
CLRF
CLRF
MOVLW
MOVWF
BSF
RETURN
BSF
BCF
INCF
MOVLW
CPFSGT
RETURN
CLRF
INCF
MOVLW
CPFSGT
RETURN
CLRF
INCF
MOVLW
CPFSGT
RETURN
CLRF
RETURN
IMPLEMENTING A REAL-TIME CLOCK USING A TIMER1 INTERRUPT SERVICE
80h
TMR1H
TMR1L
b’00001111’
T1CON
secs
mins
.12
hours
PIE1, TMR1IE
TMR1H, 7
PIR1, TMR1IF
secs, F
.59
secs
secs
mins, F
.59
mins
mins
hours, F
.23
hours
hours
; Preload TMR1 register pair
; for 1 second overflow
; Configure for external clock,
; Asynchronous operation, external oscillator
; Initialize timekeeping registers
;
; Enable Timer1 interrupt
; Preload for 1 sec overflow
; Clear interrupt flag
; Increment seconds
; 60 seconds elapsed?
; No, done
; Clear seconds
; Increment minutes
; 60 minutes elapsed?
; No, done
; clear minutes
; Increment hours
; 24 hours elapsed?
; No, done
; Reset hours
; Done
Since the register pair is 16 bits wide, a 32.768 kHz
clock source will take 2 seconds to count up to over-
flow. To force the overflow at the required one-second
intervals, it is necessary to preload it; the simplest
method is to set the MSb of TMR1H with a BSF instruc-
tion. Note that the TMR1L register is never preloaded
or altered; doing so may introduce cumulative error
over many cycles.
For this method to be accurate, Timer1 must operate in
Asynchronous mode and the Timer1 overflow interrupt
must be enabled (PIE1<0> = 1), as shown in the
routine, RTCinit. The Timer1 oscillator must also be
enabled and running at all times.
2010 Microchip Technology Inc.
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