PIC16F872-I/SP Microchip Technology Inc., PIC16F872-I/SP Datasheet - Page 22

• Manufacturer Part Number: PIC16F872-I/SP
• Description: 28 PIN, 7 KB FLASH, 128 RAM, 22 I/O
• Manufacturer: Microchip Technology Inc.

Specifications of PIC16F872-I/SP

• A/d Inputs: 5-Channel, 10-Bit
• Cpu Speed: 5 MIPS
• Eeprom Memory: 64 Bytes
• Input Output: 22
• Interface: I2C/SPI
• Memory Type: Flash
• Number Of Bits: 8
• Package Type: 28-pin SPDIP
• Programmable Memory: 3.5K Bytes
• Ram Size: 128 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

PIC16F872
2.3
The program counter (PC) is 13-bits wide. The low byte
comes from the PCL register, which is a readable and
writable register. The upper bits (PC<12:8>) are not
readable, but are indirectly writable through the
PCLATH register. On any RESET, the upper bits of the
PC will be cleared. Figure 2-3 shows the two situations
for the loading of the PC. The upper example in the fig-
ure shows how the PC is loaded on a write to PCL
(PCLATH<4:0>
ure shows how the PC is loaded during a CALL or GOTO
instruction (PCLATH<4:3>
FIGURE 2-3:
2.3.1
A computed GOTO is accomplished by adding an offset
to the program counter (ADDWF PCL). When doing a
table read using a computed GOTO method, care
should be exercised if the table location crosses a PCL
memory boundary (each 256 byte block). Refer to the
Application Note, “Implementing a Table Read"
(AN556).
DS30221C-page 20
PC
PC
12
12 11 10
2
PCL and PCLATH
5
PCH
PCLATH<4:3>
PCH
COMPUTED GOTO
PCLATH
PCLATH<4:0>
8
PCLATH
8
PCH). The lower example in the fig-
7
7
LOADING OF PC IN
DIFFERENT SITUATIONS
PCL
PCL
PCH).
11
8
0
0
Instruction with
PCL as
Destination
ALU
GOTO,CALL
Opcode <10:0>
2.3.2
The PIC16FXXX family has an 8-level deep x 13-bit
wide hardware stack. The stack space is not part of
either program or data space and the stack pointer is
not readable or writable. The PC is PUSHed onto the
stack when a CALL instruction is executed or an inter-
rupt causes a branch. The stack is POPed in the event
of a RETURN, RETLW or a RETFIE instruction execu-
tion. PCLATH is not affected by a PUSH or POP oper-
ation.
The stack operates as a circular buffer. This means that
after the stack has been PUSHed eight times, the ninth
push overwrites the value that was stored from the first
push. The tenth push overwrites the second push (and
so on).
2.4
All PIC16FXXX devices are capable of addressing a
continuous 8K word block of program memory. The
CALL and GOTO instructions provide only 11 bits of
address to allow branching within any 2K program
memory page. When doing a CALL or GOTO instruction,
the upper 2 bits of the address are provided by
PCLATH<4:3>. Since the PIC16F872 has only 2K
words of program memory or one page, additional code
is not required to ensure that the correct page is
selected before a CALL or GOTO instruction is exe-
cuted. The PCLATH<4:3> bits should always be main-
tained as zeros. If a return from a CALL instruction (or
interrupt) is executed, the entire 13-bit PC is popped off
the
PCLATH<4:3> bits are not required for the return
instructions (which POPs the address from the stack).
Note:
Note 1: There are no status bits to indicate stack
stack.
Program Memory Paging
2: There are no instructions/mnemonics
The contents of the PCLATH register are
unchanged after a RETURN or RETFIE
instruction is executed. The user must
rewrite the contents of the PCLATH regis-
ter for any subsequent subroutine calls or
GOTO instructions.
STACK
overflow or stack underflow conditions.
called PUSH or POP. These are actions
that occur from the execution of the
CALL, RETURN, RETLW and RETFIE
instructions, or the vectoring to an inter-
rupt address.
Therefore,
© 2006 Microchip Technology Inc.
manipulation
of
the