PIC16F72-E Datasheet, PDF (20/136 Pages) Microchip Technology – 28-Pin, 8-Bit CMOS FLASH Microcontoller with A/D Converter

PIC16F72
2.3 PCL and PCLATH
The program counter (PC) specifies the address of the
instruction to fetch for execution. The PC is 13-bits
wide. The low byte is called the PCL register. This reg-
ister is readable and writable. The high byte is called
the PCH register. This register contains the PC<12:8>
bits and is not directly readable or writable. All updates
to the PCH register go through the PCLATH register.
Figure 2-3 shows the four situations for the loading of
the PC.
• Example 1 shows how the PC is loaded on a write
to PCL (PCLATH<4:0> → PCH).
• Example 2 shows how the PC is loaded during a
GOTO instruction (PCLATH<4:3> → PCH).
• Example 3 shows how the PC is loaded during a
CALL instruction (PCLATH<4:3> → PCH), with
the PC loaded (PUSH’d) onto the Top-of-Stack.
• Example 4 shows how the PC is loaded during
one of the return instructions, where the PC is
loaded (POP’d) from the Top-of-Stack.
FIGURE 2-3: LOADING OF PC IN DIFFERENT SITUATIONS
Example 1 - Instruction with PCL as destination
12
PC
PCH
PCL
87
PCLATH<4:0>
5
0
8
PCLATH
ALU result
Example 2 - GOTO Instruction
PCH
PCL
12 11 10 8 7
0
PC
2 ^PCLATH<4:3>
11
Opcode <10:0>
Stack (13-bits x 8)
Top-of-Stack
Stack (13-bits x 8)
Top-of-Stack
PCLATH
Example 3 - CALL Instruction
13
PCH
12 11 10
PC
87
2 ^PCLATH<4:3>
PCL
0
11
Opcode <10:0>
PCLATH
Stack (13-bits x 8)
Top-of-Stack
Example 4 - RETURN, RETFIE, or RETLW Instruction
13
PCH
12 11 10
PC
87
PCL
0
11
Opcode <10:0>
PCLATH
Stack (13-bits x 8)
Top-of-Stack
Note: PCLATH is not updated with the contents of PCH.
DS39597C-page 18
© 2007 Microchip Technology Inc.