PIC16F1933-ESLASHP datasheet(55/418 Pages) MICROCHIP

55 / 418 page

Preliminary

DS41364A-page 53

PIC16F193X/LF193X

2.4.1

ACCESSING THE STACK

The stack is available through the TOSH, TOSL and

STKPTR registers. STKPTR is the current value of the

Stack Pointer. TOSH:TOSL register pair points to the

TOP of the stack. Both registers are read/writable. TOS

is split into TOSH and TOSL due to the 15-bit size of the

PC. To access the stack, adjust the value of STKPTR,

which will position TOSH:TOSL, then read/write to

TOSH:TOSL. STKPTR is 5 bits to allow detection of

overflow and underflow.

During normal program operation, CALL, CALLW and

Interrupts will increment STKPTR while RETURN and

RETFIE

will decrement STKPTR. At any time STKPTR

can be inspected to see how much stack is left. The

STKPTR always points at the currently used place on

the stack. Therefore, a CALL or CALLW will write the

PC and then increment the STKPTR, and a return will

decrement the PC and then unload the PC.

2.4.2

OVERFLOW/UNDERFLOW RESET

If the STVREN bit in Configuration Word 2 is

programmed, the device will be reset if the stack is

PUSHed beyond the sixteenth level or POPed beyond

the first level, setting the appropriate bits (STKOVF or

STKUNF, respectively) in the PCON register.

2.5

Indirect Addressing, INDF and

FSR Registers

The INDFn registers are not physical registers. Any

instruction that accesses an INDFn register actually

accesses the register at the address specified by the

File Select Registers (FSR). If the FSRn address

specifies one of the two INDFn registers, the read will

return ‘0’ and the write will not occur (though Status bits

may be affected). The FSRn register value is created

by the pair FSRnH and FSRnL.

The FSR registers form a 16-bit address that allows an

addressing space with 65536 locations. These locations

are divided into three memory regions:

• Traditional Data Memory

• Linear Data Memory

• Program Flash Memory

PIC16F1933-E/P Datasheet(PDF) 55 Page - Microchip Technology

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