PIC16F747 Microchip Technology Inc., PIC16F747 Datasheet - Page 31

• Manufacturer Part Number: PIC16F747
• Description: 28/40/44-pin, 8-bit Cmos Flash Microcontrollers With 10-bit A/d And Nanowatt Technology
• Manufacturer: Microchip Technology Inc.

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 2-4 shows the two situations
for the loading of the PC. The upper example in the
figure shows how the PC is loaded on a write to PCL
(PCLATH<4:0>
figure shows how the PC is loaded during a CALL or
GOTO instruction (PCLATH<4:3>
FIGURE 2-4:
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, AN556 “Implementing a Table Read”
(DS00556).
2.3.2
The PIC16F7X7 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
interrupt causes a branch. The stack is POPed in the
event of a RETURN, RETLW or a RETFIE instruction
execution. PCLATH is not affected by a PUSH or POP
operation.
 2004 Microchip Technology Inc.
PC
PC
12
12 11 10
2
PCL and PCLATH
PCH
5
PCLATH<4:3>
PCH
COMPUTED GOTO
STACK
PCLATH
PCLATH<4:0>
8
PCLATH
8
7
PCH). The lower example in the
7
LOADING OF PC IN
DIFFERENT SITUATIONS
PCL
PCL
11
8
PCH).
0
0
Instruction with
PCL as
Destination
ALU
GOTO,CALL
Opcode <10:0>
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
PIC16F7X7 devices are capable of addressing a con-
tinuous 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>.
When doing a CALL or GOTO instruction, the user must
ensure that the page select bits are programmed so
that the desired program memory page is addressed. If
a return from a CALL instruction (or interrupt) is
executed, the entire 13-bit PC is POPed off the stack.
Therefore, manipulation of the PCLATH<4:3> bits is
not required for the RETURN instructions (which POPs
the address from the stack).
Example 2-1 shows the calling of a subroutine in
page 1 of the program memory. This example assumes
that PCLATH is saved and restored by the Interrupt
Service Routine (if interrupts are used).
EXAMPLE 2-1:
SUB1_P1
RETURN
Note:
Note 1: There are no Status bits to indicate stack
2: There are no instructions/mnemonics
Program Memory Paging
ORG
BCF
BSF
:
:
ORG
:
:
:
CALL SUB1_P1
The
unchanged after a RETURN or RETFIE
instruction is executed. The user must set
up the PCLATH for any subsequent CALLs
or GOTOs.
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
interrupt address.
0x500
PCLATH, 4
PCLATH, 3 ;Select page 1
0x900
contents
CALL OF A SUBROUTINE
IN PAGE 1 FROM PAGE 0
PIC16F7X7
;(800h-FFFh)
;Call subroutine in
;page 1 (800h-FFFh)
;page 1 (800h-FFFh)
;called subroutine
;page 1 (800h-FFFh)
;return to Call
;subroutine in page 0
;(000h-7FFh)
of
the
DS30498C-page 29
PCLATH
are