PIC17C44 Datasheet, PDF(29/241 Page) Microchip Technology – High-Performance 8-Bit CMOS EPROM/ROM Microcontroller

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PIC17C44 Datasheet, PDF (29/241 Pages) Microchip Technology – High-Performance 8-Bit CMOS EPROM/ROM Microcontroller

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6.0 MEMORY ORGANIZATION

There are two memory blocks in the PIC17C4X; pro-

gram memory and data memory. Each block has its

own bus, so that access to each block can occur during

the same oscillator cycle.

The data memory can further be broken down into Gen-

eral Purpose RAM and the Special Function Registers

(SFRs). The operation of the SFRs that control the

âcoreâ are described here. The SFRs used to control

the peripheral modules are described in the section dis-

cussing each individual peripheral module.

6.1 Program Memory Organization

PIC17C4X devices have a 16-bit program counter

capable of addressing a 64K x 16 program memory

space. The reset vector is at 0000h and the interrupt

vectors are at 0008h, 0010h, 0018h, and 0020h

(Figure 6-1).

6.1.1 PROGRAM MEMORY OPERATION

The PIC17C4X can operate in one of four possible pro-

gram memory conï¬gurations. The conï¬guration is

selected by two conï¬guration bits. The possible modes

are:

â¢ Microprocessor

â¢ Microcontroller

â¢ Extended Microcontroller

â¢ Protected Microcontroller

The microcontroller and protected microcontroller

modes only allow internal execution. Any access

beyond the program memory reads unknown data.

The protected microcontroller mode also enables the

code protection feature.

The extended microcontroller mode accesses both the

internal program memory as well as external program

memory. Execution automatically switches between

internal and external memory. The 16-bits of address

allow a program memory range of 64K-words.

The microprocessor mode only accesses the external

program memory. The on-chip program memory is

ignored. The 16-bits of address allow a program mem-

ory range of 64K-words. Microprocessor mode is the

default mode of an unprogrammed device.

The different modes allow different access to the con-

ï¬guration bits, test memory, and boot ROM. Table 6-1

lists which modes can access which areas in memory.

Test Memory and Boot Memory are not required for

normal operation of the device. Care should be taken to

ensure that no unintended branches occur to these

areas.

PIC17C4X

FIGURE 6-1: PROGRAM MEMORY MAP

AND STACK

PC<15:0>

CALL, RETURN

16

RETFIE, RETLW

Stack Level 1

â¢â¢â¢

Stack Level 16

Reset Vector

0000h

INT Pin Interrupt Vector 0008h

Timer0 Interrupt Vector 0010h

T0CKI Pin Interrupt Vector 0018h

Peripheral Interrupt Vector 0020h

0021h

7FFh

(PIC17C42,

PIC17CR42,

PIC17C42A)

FFFh

(PIC17C43

PIC17CR43)

1FFFh

(PIC17C44)

FOSC0

FOSC1

WDTPS0

WDTPS1

PM0

Reserved

PM1

Reserved

Reserved

PM2(2)

Test EPROM

Boot ROM

FDFFh

FE00h

FE01h

FE02h

FE03h

FE04h

FE05h

FE06h

FE07h

FE08h

FE0Eh

FE0Fh

FE10h

FF5Fh

FF60h

FFFFh

Note 1:

2:

User memory space may be internal, external, or

both. The memory conï¬guration depends on the

processor mode.

This location is reserved on the PIC17C42.

Â© 1996 Microchip Technology Inc.

This document was created with FrameMaker 4 0 4

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