PIC18LF4331-ESLASHML datasheet(63/392 Pages) MICROCHIP

63 / 392 page

 2010 Microchip Technology Inc.

DS39616D-page 63

PIC18F2331/2431/4331/4431

When the stack has been popped enough times to

unload the stack, the next pop will return a value of zero

to the PC and set the STKUNF bit, while the Stack

Pointer remains at zero. The STKUNF bit will remain

set until cleared by software or a POR occurs.

FIGURE 6-3:

RETURN ADDRESS STACK AND ASSOCIATED REGISTERS

Note:

Returning a value of zero to the PC on an

underflow has the effect of vectoring the

program to the Reset vector, where the

stack conditions can be verified and

appropriate actions can be taken. This is

not the same as a Reset as the contents

of the SFRs are not affected.

STKPTR: STACK POINTER REGISTER

R/C-0

U-0

R/W-0

STKFUL(1)

STKUNF(1)

—

SP4

SP3

SP2

SP1

SP0

bit 7

bit 0

Legend:

C = Clearable bit

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

-n = Value at POR

‘1’ = Bit is set

‘0’ = Bit is cleared

x = Bit is unknown

bit 7

STKFUL:

Stack Full Flag bit(1)

= Stack became full or overflowed

= Stack has not become full or overflowed

bit 6

STKUNF:

Stack Underflow Flag bit(1)

= Stack underflow occurred

= Stack underflow did not occur

bit 5

Unimplemented:

Read as ‘0’

bit 4-0

SP<4:0>:

Stack Pointer Location bits

Note 1:

Bit 7 and bit 6 are cleared by user software or by a POR.

00011

001A34h

11111

11110

11101

00010

00001

00000

00010

Return Address Stack

Top-of-Stack

000D58h

TOSL

TOSH

TOSU

34h

1Ah

00h

STKPTR<4:0>

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