参数资料
型号: PIC16C621-20/SS
元件分类: 微控制器/微处理器
英文描述: 8-BIT, OTPROM, 20 MHz, RISC MICROCONTROLLER, PDSO20
封装: 0.209 INCH, PLASTIC, MO-150, SSOP-20
文件页数: 38/121页
文件大小: 1202K
代理商: PIC16C621-20/SS
1999 Microchip Technology Inc.
DS30235H-page 23
PIC16C62X
4.3
PCL and PCLATH
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 4-8 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>
→ PCH). The lower example in the figure
shows how the PC is loaded during a CALL or GOTO
instruction (PCLATH<4:3>
→ PCH).
FIGURE 4-8:
LOADING OF PC IN
DIFFERENT SITUATIONS
4.3.1
COMPUTED GOTO
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
12
8
7
0
5
PCLATH<4:0>
PCLATH
Instruction with
ALU result
GOTO,CALL
Opcode <10:0>
8
PC
12
11 10
0
11
PCLATH<4:3>
PCH
PCL
87
2
PCLATH
PCH
PCL
PCL as
Destination
4.3.2
STACK
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 RET-
FIE
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:
There are no STATUS bits to indicate
stack
overflow
or
stack
underflow
conditions.
Note 2:
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.
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