User`s guide

External Memory Handling

5.2.5 External Memory Interface

The External Memory Interface is a feature that allows the microcontroller to access

external memory devices (such as Flash, EPROM, SRAM, etc.) as program or data

memory.

PIC17 Devices

When either Microprocessor or Extended Microcontroller mode is selected, PORTC,

PORTD and PORTE are configured as the system bus. PORTC and PORTD are the

multiplexed address/data bus and PORTE<2:0> is for the control signals. External

components are needed to demultiplex the address and data.

For more information, see the Memory Organization, External Memory Interface

section of the device data sheet.

PIC18 Devices

Using the MEMCON register, the following may be configured:

• External bus enable and disable

• 16-Bit mode – Word Write mode, Byte Select mode or Byte Write mode

• Wait – Table read/write bus cycle wait counts (0-3 T

CY)

For more information, see the External Memory Interface section of the device data

sheet.

5.3 EXTERNAL MEMORY ENABLED IN MPLAB IDE

To set up MPLAB IDE (and a selected debug tool) to recognize external memory, select

Configure>External Memory

. Then check “Use External Memory” and enter a range.

See Section 13.9 “External Memory Setting Dialog” for more on this dialog.

Some debug tools may require additional setup for external memory, usually on the

Debugger>Settings

dialog. See the documentation for the tool for more information.

5.4 PROGRAM MEMORY WINDOW

The Program Memory window will contain all enabled program memory, i.e., on-chip,

external or a combination of both. See Section 12.8 “Program Memory Window” for