PIC16F636T-I/SL(2005) View Datasheet(PDF) - Microchip Technology

Part Name

Description

Manufacturer

PIC16F636T-I/SL
(Rev.:2005)

8/14-Pin Flash-Based, 8-Bit CMOS Microcontrollers with nanoWatt Technology

Microchip Technology 

PIC12F635/PIC16F636/639

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 2-5 shows the

two situations for the loading of the PC. The upper

example in Figure 2-5 shows how the PC is loaded on a

write to PCL (PCLATH<4:0> → PCH). The lower

example in Figure 2-5 shows how the PC is loaded

during a CALL or GOTO instruction (PCLATH<4:3> →

PCH).

FIGURE 2-5:

LOADING OF PC IN

DIFFERENT SITUATIONS

12

PC

PCH

PCL

87

PCLATH<4:0>

5

Instruction with

0

PCL as

Destination

8

ALU Result

PCLATH

PCH

12 11 10

PC

87

2 PCLATH<4:3>

PCL

0

GOTO, CALL

11

Opcode<10:0>

PCLATH

2.3.1 COMPUTED GOTO

A computed GOTO is accomplished by adding an offset

to the program counter (ADDWF PCL). When

performing 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 STACK

The PIC12F635/PIC16F636/639 family has 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 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: 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.

DS41232B-page 26

Preliminary

© 2005 Microchip Technology Inc.

Share Link: