PIC10LF320 View Datasheet(PDF) - Microchip Technology
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MFG CO.
'PIC10LF320' PDF : 210 Pages View PDF
2.3 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 2-3 shows the two
situations for the loading of the PC. The upper example
in Figure 2-3 shows how the PC is loaded on a write to
PCL (PCLATH<4:0> PCH). The lower example in
Figure 2-3 shows how the PC is loaded during a CALL or
GOTO instruction (PCLATH<4:3> PCH).
FIGURE 2-3:
LOADING OF PC IN
DIFFERENT SITUATIONS
12
PC
PCH
PCL
87
5
PCLATH<4:0>
0
8
Instruction with
PCL as
Destination
ALU Result
PCLATH
12
PC
PCH
11 10
87
2
PCLATH<4:3>
PCL
0
GOTO, CALL
11
OPCODE <10:0>
PCLATH
2.3.1 MODIFYING PCL
Executing any instruction with the PCL register as the
destination simultaneously causes the Program
Counter PC<12:8> bits (PCH) to be replaced by the
contents of the PCLATH register. This allows the entire
contents of the program counter to be changed by
writing the desired upper five bits to the PCLATH
register. When the lower eight bits are written to the
PCL register, all 13 bits of the program counter will
change to the values contained in the PCLATH register
and those being written to the PCL register.
A computed GOTO is accomplished by adding an offset
to the program counter (ADDWF PCL). Care should be
exercised when jumping into a look-up table or
program branch table (computed GOTO) by modifying
the PCL register. Assuming that PCLATH is set to the
table start address, if the table length is greater than
255 instructions or if the lower eight bits of the memory
address rolls over from 0xFF to 0x00 in the middle of
the table, then PCLATH must be incremented for each
address rollover that occurs between the table
beginning and the target location within the table.
For more information refer to Application Note AN556,
“Implementing a Table Read” (DS00556).
PIC10(L)F320/322
2.3.2 STACK
All devices have an 8-level x 13-bit wide hardware
stack (see Figure 2-1). 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
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.
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.
2.4 Indirect Addressing, INDF and
FSR Registers
The INDF register is not a physical register. Addressing
the INDF register will cause indirect addressing.
Indirect addressing is possible by using the INDF
register. Any instruction using the INDF register
actually accesses data pointed to by the File Select
Register (FSR). Reading INDF itself indirectly will
produce 00h. Writing to the INDF register indirectly
results in a no operation (although Status bits may be
affected). An effective 9-bit address is obtained by
concatenating the 8-bit FSR and the IRP bit of the
STATUS register, as shown in Figure 2-4.
A simple program to clear RAM location 40h-7Fh using
indirect addressing is shown in Example 2-1.
EXAMPLE 2-1: INDIRECT ADDRESSING
MOVLW
MOVWF
NEXT CLRF
INCF
BTFSS
GOTO
CONTINUE
0x40
FSR
INDF
FSR
FSR,7
NEXT
;initialize pointer
;to RAM
;clear INDF register
;inc pointer
;all done?
;no clear next
;yes continue
2011-2015 Microchip Technology Inc.
DS40001585D-page 17
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