PIC16C620 Microchip Technology, PIC16C620 Datasheet - Page 23

• Manufacturer Part Number: PIC16C620
• Description: EPROM-Based 8-Bit CMOS Microcontroller
• Manufacturer: Microchip Technology

4.3
The program counter (PC) is 13-bits wide. The low byte
comes from the PCL register, which is a readable and
writable register. The high byte (PC<12:8>) is not directly
readable or writable and comes from PCLATH. On any
reset, the PC is cleared. Figure 4-14 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>
shows how the PC is loaded during a CALL or GOTO
instruction (PCLATH<4:3>
FIGURE 4-14: LOADING OF PC IN
4.3.1
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).
PC
PC
1998 Microchip Technology Inc.
12
12 11 10
2
PCL and PCLATH
COMPUTED GOTO
5
PCH
PCLATH<4:3>
PCH
PCLATH
PCLATH<4:0>
8
PCLATH
8
PCH). The lower example in the figure
DIFFERENT SITUATIONS
7
7
PCL
PCL
PCH).
11
8
0
0
Instruction with
PCL as
Destination
ALU result
GOTO, CALL
Opcode <10:0>
Preliminary
4.3.2
The PIC16C62X family has an 8 level deep x 13-bit
wide hardware stack (Figure 4-2 and Figure 4-3). 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.
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).
Note 1:
Note 2:
STACK
There are no STATUS bits to indicate
stack overflow or stack underflow
conditions.
There are no instructions/mnemonics
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.
PIC16C62X
DS30235G-page 23