PIC18F448-I/PT Microchip Technology, PIC18F448-I/PT Datasheet - Page 42

• Manufacturer Part Number: PIC18F448-I/PT
• Description: IC PIC MCU FLASH 8KX16 44TQFP
• Manufacturer: Microchip Technology
• Series: PIC® 18Fr

Specifications of PIC18F448-I/PT

• Core Size: 8-Bit
• Program Memory Size: 16KB (8K x 16)
• Core Processor: PIC
• Speed: 40MHz
• Connectivity: CAN, I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, LVD, POR, PWM, WDT
• Number Of I /o: 33
• Program Memory Type: FLASH
• Eeprom Size: 256 x 8
• Ram Size: 768 x 8
• Voltage - Supply (vcc/vdd): 4.2 V ~ 5.5 V
• Data Converters: A/D 8x10b
• Oscillator Type: External
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 44-TQFP, 44-VQFP
• Controller Family/series: PIC18
• No. Of I/o's: 33
• Eeprom Memory Size: 256Byte
• Ram Memory Size: 768Byte
• Cpu Speed: 40MHz
• No. Of Timers: 4
• Processor Series: PIC18F
• Core: PIC
• Data Bus Width: 8 bit
• Data Ram Size: 768 B
• Interface Type: SPI, I2C, USART
• Maximum Clock Frequency: 40 MHz
• Number Of Programmable I/os: 33
• Number Of Timers: 4 bit
• 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, 52712-325, EWPIC18
• Development Tools By Supplier: PG164130, DV164035, DV244005, DV164005, PG164120, ICE2000, DV164136, DM163011
• Minimum Operating Temperature: - 40 C
• On-chip Adc: 8
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: XLT44PT3 - SOCKET TRAN ICE 44MQFP/TQFPAC164305 - MODULE SKT FOR PM3 44TQFP444-1001 - DEMO BOARD FOR PICMICRO MCUAC164020 - MODULE SKT PROMATEII 44TQFP
• Lead Free Status / Rohs Status: Details

4.2.3
Since the Top-of-Stack (TOS) is readable and writable,
the ability to push values onto the stack and pull values
off the stack, without disturbing normal program execu-
tion, is a desirable option. To push the current PC value
onto the stack, a PUSH instruction can be executed.
This will increment the Stack Pointer and load the
current PC value onto the stack. TOSU, TOSH and
TOSL can then be modified to place a return address
on the stack.
The POP instruction discards the current TOS by decre-
menting the Stack Pointer. The previous value pushed
onto the stack then becomes the TOS value.
4.2.4
These Resets are enabled by programming the
STVREN configuration bit. When the STVREN bit is
disabled, a full or underflow condition will set the appro-
priate STKFUL or STKUNF bit, but not cause a device
Reset. When the STVREN bit is enabled, a full or
underflow condition will set the appropriate STKFUL or
STKUNF bit and then cause a device Reset. The
STKFUL or STKUNF bits are only cleared by the user
software or a POR.
4.3
A “fast return” option is available for interrupts and
calls. A fast register stack is provided for the Status,
WREG and BSR registers and is only one layer in
depth. The stack is not readable or writable and is
loaded with the current value of the corresponding
register when the processor vectors for an interrupt.
The values in the fast register stack are then loaded
back into the working registers if the FAST RETURN
instruction is used to return from the interrupt.
A low or high priority interrupt source will push values
into the stack registers. If both low and high priority
interrupts are enabled, the stack registers cannot be
used reliably for low priority interrupts. If a high priority
interrupt occurs while servicing a low priority interrupt,
the stack register values stored by the low priority
interrupt will be overwritten.
If high priority interrupts are not disabled during low
priority interrupts, users must save the key registers in
software during a low priority interrupt.
If no interrupts are used, the fast register stack can be
used to restore the Status, WREG and BSR registers at
the end of a subroutine call. To use the fast register
stack for a subroutine call, a FAST CALL instruction
must be executed.
Example 4-1 shows a source code example that uses
the fast register stack.
DS41159E-page 40
PIC18FXX8
Fast Register Stack
PUSH AND POP INSTRUCTIONS
STACK FULL/UNDERFLOW RESETS
EXAMPLE 4-1:
4.4
The Program Counter (PC) specifies the address of the
instruction to fetch for execution. The PC is 21 bits
wide. The low byte is called the PCL register. This reg-
ister is readable and writable. The high byte is called
the PCH register. This register contains the PC<15:8>
bits and is not directly readable or writable. Updates to
the PCH register may be performed through the
PCLATH register. The upper byte is called PCU. This
register contains the PC<20:16> bits and is not directly
readable or writable. Updates to the PCU register may
be performed through the PCLATU register.
The PC addresses bytes in the program memory. To
prevent the PC from becoming misaligned with word
instructions, the LSb of PCL is fixed to a value of ‘0’.
The PC increments by 2 to address sequential
instructions in the program memory.
The CALL,
instructions write to the program counter directly. For
these instructions, the contents of PCLATH and
PCLATU are not transferred to the program counter.
The contents of PCLATH and PCLATU will be
transferred to the program counter by an operation that
writes PCL. Similarly, the upper two bytes of the
program counter will be transferred to PCLATH and
PCLATU by an operation that reads PCL. This is useful
for computed offsets to the PC (see Section 4.8.1
“Computed GOTO”).
CALL SUB1, FAST
SUB1
RETURN FAST
PCL, PCLATH and PCLATU
RCALL,
FAST REGISTER STACK
CODE EXAMPLE
;STATUS, WREG, BSR
;SAVED IN FAST REGISTER
;STACK
;RESTORE VALUES SAVED
;IN FAST REGISTER STACK
© 2006 Microchip Technology Inc.
GOTO and program branch