DM163006 datasheet(67/320 Pages) MICROCHIP

67 / 320 page

 2001 Microchip Technology Inc.

Advance Information

DS39541A-page 67

PIC18C601/801

5.3

16-bit Mode

The External Memory Interface can operate in 16-bit

mode. The mode selection is not software configurable,

but is programmable via the configuration bits.

The WM<1:0> bits in the MEMCON register determine

three types of connections in 16-bit mode. They are

referred to as:

• 16-bit Byte Write

• 16-bit Word Write

• 16-bit Byte Select

These three different configurations allow the designer

maximum flexibility in using 8-bit and 16-bit memory

devices.

For all 16-bit modes, the Address Latch Enable (ALE)

pin indicates that the address bits A<15:0> are avail-

able on the External Memory Interface bus. Following

the address latch, the output enable signal (OE ) will

enable both bytes of program memory at once to form

a 16-bit instruction word.

In Byte Select mode, JEDEC standard FLASH memo-

ries will require BA0 for the byte address line, and one

I/O line, to select between byte and word mode. The

other 16-bit modes do not need BA0. JEDEC standard

static RAM memories will use the UB or UL signals for

byte selection.

5.3.1

16-BIT BYTE WRITE MODE

Figure 5-5 shows an example of 16-bit Byte Write

mode for the PIC18C601/801.

FIGURE 5-5:

16-BIT BYTE WRITE MODE EXAMPLE

AD<15:8>

A<19:16>

ALE

D<7:0>

373

A<x:0>

D<7:0>

A<19:0>

A<x:0>

D<7:0>

373

WRH

WR(1)

Note 1: This signal only applies to Table Writes. See Section 6.0, Table Reads and Writes.

WRL

D<15:8>

(LSB)

(MSB)

PIC18C801

D<7:0>

AD<7:0>

CS1

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