DM163006 datasheet(63/320 Pages) MICROCHIP

63 / 320 page

 2001 Microchip Technology Inc.

Advance Information

DS39541A-page 63

PIC18C601/801

5.0

EXTERNAL MEMORY

INTERFACE

The External Memory Interface is a feature of the

PIC18C601/801 that allows the processor to access

external memory devices, such as FLASH, EPROM,

SRAM, etc. Memory mapped peripherals may also be

accessed.

The External Memory Interface physical implementa-

tion includes up to 26 pins on the PIC18C601 and up to

38 pins on the PIC18C801. These pins are reserved for

external address/data bus functions.

These pins are multiplexed with I/O port pins, but the

I/O functions are only enabled when program execution

takes place in internal Boot RAM and the EBDIS bit in

the MEMCON register is set (see Register 5-1).

5.1

Memory Control Register

(MEMCON)

(MEMCON). This register contains bits used to control

the operation of the External Memory Interface.

MEMCON REGISTER

R/W-0

U-0

R/W-0

EBDIS

PGRM

WAIT1

WAIT0

—

WM1

WM0

bit7

bit0

bit 7

EBDIS: External Bus Disable

= External system bus disabled, all external bus drivers are mapped as I/O ports

= External system bus enabled, and I/O ports are disabled

bit 6

PGRM: Program RAM Enable

= 512 bytes of internal RAM enabled as internal program memory from location 1FFE00h to

1FFFFFh, external program memory at these locations is unused. Internal GPR memory

from 400h to 5FFh is disabled and returns 00h.

= Internal RAM enabled as internal GPR memory from 400h to 5FFh. Program memory from

location 1FFE00h to 1FFFFFh is configured as external program memory.

bit 5-4

WAIT<1:0>: Table Reads and Writes Bus Cycle Wait Count

= Table reads and writes will wait 0 TCY

= Table reads and writes will wait 1 TCY

= Table reads and writes will wait 2 TCY

= Table reads and writes will wait 3 TCY

bit 3-2

Unimplemented: Read as '0'

bit 1-0

WM<1:0>: TABLWT Operation with 16-bit Bus

= Word Write mode: TABLAT0 and TABLAT1 word output, WRH active when TABLAT1 written

= Byte Select mode: TABLAT data copied on both MS and LS Byte, WRH and (UB or LB) will

activate

= Byte Write mode: TABLAT data copied on both MS and LS Byte, WRH or WRL will activate

Legend:

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

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