PIC18F4585-H/PT Microchip Technology, PIC18F4585-H/PT Datasheet - Page 155

• Manufacturer Part Number: PIC18F4585-H/PT
• Description: IC MCU 8BIT 48KB FLASH 44TQFP
• Manufacturer: Microchip Technology
• Series: PIC® 18Fr

Specifications of PIC18F4585-H/PT

• Core Processor: PIC
• Core Size: 8-Bit
• Speed: 25MHz
• Connectivity: CAN, I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, HLVD, POR, PWM, WDT
• Number Of I /o: 36
• Program Memory Size: 48KB (24K x 16)
• Program Memory Type: FLASH
• Eeprom Size: 1K x 8
• Ram Size: 3.25K x 8
• Voltage - Supply (vcc/vdd): 4.2 V ~ 5.5 V
• Data Converters: A/D 11x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 150°C
• Package / Case: 44-TQFP
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

12.2
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 register. 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, has become invalid due to a rollover between
reads.
A write to the high byte of Timer1 must also take place
through the TMR1H Buffer register. The 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
writable 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.
12.3
An on-chip crystal oscillator circuit is incorporated
between pins T1OSI (input) and T1OSO (amplifier
output). It is enabled by setting the Timer1 Oscillator
Enable bit, T1OSCEN (T1CON<3>). The oscillator is a
low-power circuit rated for 32 kHz crystals. It will
continue to run during all power managed modes. The
circuit for a typical LP oscillator is shown in Figure 12-3.
Table 12-1 shows the capacitor selection for the Timer1
oscillator.
The user must provide a software time delay to ensure
proper start-up of the Timer1 oscillator.
FIGURE 12-3:
© 2007 Microchip Technology Inc.
Note:
Timer1 16-Bit Read/Write Mode
Timer1 Oscillator
33 pF
33 pF
C1
C2
See the Notes with Table 12-1 for additional
information about capacitor selection.
32.768 kHz
XTAL
EXTERNAL
COMPONENTS FOR THE
TIMER1 LP OSCILLATOR
T1OSI
T1OSO
PIC18FXXXX
PIC18F2585/2680/4585/4680
Preliminary
TABLE 12-1:
12.3.1
The Timer1 oscillator is also available as a clock source
in power managed modes. By setting the clock select
bits, SCS1:SCS0 (OSCCON<1:0>), to ‘01’, the device
switches to SEC_RUN mode; both the CPU and
peripherals are clocked from the Timer1 oscillator. If the
IDLEN bit (OSCCON<7>) is cleared and a SLEEP
instruction is executed, the device enters SEC_IDLE
mode. Additional details are available in Section 3.0
“Power Managed Modes”.
Whenever the Timer1 oscillator is providing the clock
source, the Timer1 system clock status flag, T1RUN
(T1CON<6>), is set. This can be used to determine the
controller’s current clocking mode. It can also indicate
the clock source being currently used by the Fail-Safe
Clock Monitor. If the Clock Monitor is enabled and the
Timer1 oscillator fails while providing the clock, polling
the T1RUN bit will indicate whether the clock is being
provided by the Timer1 oscillator or another source.
12.3.2
The Timer1 oscillator can operate at two distinct levels
of power consumption based on device configuration.
When the LPT1OSC Configuration bit is set, the Timer1
oscillator operates in a low-power mode. When
LPT1OSC is not set, Timer1 operates at a higher power
level. Power consumption for a particular mode is rela-
tively constant, regardless of the device’s operating
mode. The default Timer1 configuration is the higher
power mode.
As the low-power Timer1 mode tends to be more
sensitive to interference, high noise environments may
cause some oscillator instability. The low-power option is,
therefore, best suited for low noise applications where
power conservation is an important design consideration.
Osc Type
Note 1: Microchip suggests these values as a
LP
2: Higher capacitance increases the stability
3: Since each resonator/crystal has its own
4: Capacitor values are for design guidance
USING TIMER1 AS A CLOCK
SOURCE
LOW-POWER TIMER1 OPTION
starting point in validating the oscillator
circuit.
of the oscillator but also increases the
start-up time.
characteristics, the user should consult
the resonator/crystal manufacturer for
appropriate
components.
only.
32 kHz
Freq
CAPACITOR SELECTION
FOR THE TIMER
OSCILLATOR
values
27 pF
C1
(1,2,3,4)
DS39625C-page 153
of
27 pF
external
C2