PIC18F4431-I/P Microchip Technology Inc., PIC18F4431-I/P Datasheet - Page 142
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PIC18F4431-I/P
Manufacturer Part Number
PIC18F4431-I/P
Description
Microcontroller; 16 KB Flash; 768 RAM; 256 EEPROM; 36 I/O; 40-Pin-PDIP
Manufacturer
Microchip Technology Inc.
Datasheet
1.PIC18F4431-IP.pdf
(396 pages)
Specifications of PIC18F4431-I/P
A/d Inputs
9-Channel, 10-Bit
Cpu Speed
10 MIPS
Eeprom Memory
256 Bytes
Input Output
36
Interface
I2C/SPI/USART
Memory Type
Flash
Number Of Bits
8
Package Type
40-pin PDIP
Programmable Memory
16K Bytes
Ram Size
768 Bytes
Speed
40 MHz
Timers
1-8-bit, 3-16-bit
Voltage, Range
2-5.5 V
Lead Free Status / Rohs Status
RoHS Compliant part
Electrostatic Device
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PIC18F2331/2431/4331/4431
12.4
The TMR1 register pair (TMR1H:TMR1L) increments
from 0000h to FFFFh and rolls over to 0000h. The
Timer1 interrupt, if enabled, is generated on overflow,
which is latched in interrupt flag bit, TMR1IF
(PIR1<0>). This interrupt can be enabled/disabled by
setting/clearing Timer1 interrupt enable bit, TMR1IE
(PIE1<0>).
12.5
If the CCP module is configured in Compare mode to
generate a “special event trigger” (CCP1M3:CCP1M0
= 1011), this signal will reset Timer1 and start an A/D
conversion if the A/D module is enabled (see
Section 15.4.4 “Special Event Trigger” for more
information.).
Timer1 must be configured for either Timer or Synchro-
nized Counter mode to take advantage of this feature.
If Timer1 is running in Asynchronous Counter mode,
this Reset operation may not work.
In the event that a write to Timer1 coincides with a
special event trigger from CCP1, the write will take
precedence.
In this mode of operation, the CCPR1H:CCPR1L regis-
ters pair effectively becomes the period register for
Timer1.
12.6
Timer1 can be configured for 16-bit reads and writes
(see Figure 12-2). When the RD16 control bit
(T1CON<7>) is set, the address for TMR1H is mapped
to a buffer register for the high byte of Timer1. A read
from TMR1L will load the contents of the high byte of
Timer1 into the Timer1 high byte buffer. This provides
the user with the ability to accurately read all 16 bits of
Timer1 without having to determine whether a read of
the high byte, followed by a read of the low byte, is
valid, due to a rollover between reads.
A write to the high byte of Timer1 must also take place
through the TMR1H buffer register. Timer1 high byte is
updated with the contents of TMR1H when a write
occurs to TMR1L. This allows a user to write all 16 bits
to both the high and low bytes of Timer1 at once.
The high byte of Timer1 is not directly readable or writ-
able in this mode. All reads and writes must take place
through the Timer1 high byte buffer register. Writes to
TMR1H do not clear the Timer1 prescaler. The
prescaler is only cleared on writes to TMR1L.
DS39616B-page 140
Note:
Timer1 Interrupt
Resetting Timer1 Using a CCP
Trigger Output
Timer1 16-Bit Read/Write Mode
The special event triggers from the CCP1
module will not set interrupt flag bit
TMR1IF (PIR1<0>).
Preliminary
12.7
Adding an external LP oscillator to Timer1 (such as the
one described in Section 12.2 “Timer1 Oscillator”),
gives users the option to include RTC functionality 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 12-1, 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 as the previous counter overflow.
Since the register pair is 16-bits wide, counting up to
overflow the register directly from a 32.768 kHz clock
would take 2 seconds. To force the overflow at the
required one-second intervals, it is necessary to pre-
load it; the simplest method is to set the MSbit of
TMR1H with a BSF instruction. 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 rou-
tine RTCinit. The Timer1 oscillator must also be
enabled and running at all times.
Using Timer1 as a Real-Time
Clock
2003 Microchip Technology Inc.
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