User`s guide

MPLAB

IDE

USER’S GUIDE

Chapter 5. External Memory Handling

5.1 INTRODUCTION

Some Microchip devices allow the extension or replacement of program memory

resources with external (off-chip) memory devices. MPLAB IDE handles this device

feature as described here.

• Configuration Bits and External Memory Setup

• External Memory Enabled in MPLAB IDE

• Program Memory Window

5.2 CONFIGURATION BITS AND EXTERNAL MEMORY SETUP

A device that supports external memory must be set up to use external memory via the

device Configuration bits.

For PIC17CXXX and PIC18F6XXX/8XXX devices, a Program Memory mode is set by

using Configuration bits. Depending on the device, the Processor Mode Select bits are

located in a configuration register which is programmed when the device is

programmed.

For PIC18C601/801 devices, External Bus Data Width is set as a Configuration bit.

To set the values of Configuration bits for your selected device, open the Configuration

Bits window by selecting Configure>Configuration Bits

. In the Category column, find

the bits you need to set and click on them to change their value. See

Section 12.21 “Configuration Bits Window” for more information on this window.

Information on device memory modes and the external bus is provided below. For more

information, consult the device data sheet.

5.2.1 PIC17CXXX Program Memory Modes

PIC17CXXX devices are capable of operating in any one of several program memory

modes, using combinations of on-chip and external program memory. Available

program memory modes are as follows:

• The Microprocessor mode permits access only to external program memory; the

contents of the on-chip program memory are ignored. The program counter

permits access to a linear program memory space and defines the amount of

accessible program memory (see Section 5.2.4 “Program Counter”).

Microprocessor mode is the default mode of an unprogrammed device.

• The Microcontroller and Protected Microcontroller modes access only on-chip

program memory. Attempts to read above the physical limit of the on-chip memory

results in unknown data. The Protected Microcontroller mode also enables the

code protection feature.

Note: Configuration bits may also be set in code using __config. Refer to the

device data sheet and header file (.inc or .h) for more information.