PIC18F6X2X datasheet(78/386 Pages) MICROCHIP

78 / 386 page

PIC18F6X2X/8X2X

DS39612A-page 76

Advance Information

 2003 Microchip Technology Inc.

6.2.2

16-BIT WORD WRITE MODE

Figure 6-2 shows an example of 16-bit Word Write

mode for PIC18F8X2X devices. This mode is used for

word-wide memories which includes some of the

EPROM and FLASH type memories. This mode allows

opcode fetches and table reads from all forms of 16-bit

memory, and table writes to any type of word-wide

external memories. This method makes a distinction

between TBLWT cycles to even or odd addresses.

During

TBLWT

cycle

even

address

(TBLPTR<0> = 0), the TABLAT data is transferred to a

holding latch and the external address data bus is tri-

stated for the data portion of the bus cycle. No write

signals are activated.

During

TBLWT

cycle

odd

address

(TBLPTR<0> = 1), the TABLAT data is presented on

the upper byte of the AD15:AD0 bus. The contents of

the holding latch are presented on the lower byte of the

AD15:AD0 bus.

The WRH signal is strobed for each write cycle; the

WRL pin is unused. The signal on the BA0 pin indicates

the LSbit of the TBLPTR but it is left unconnected.

Instead, the UB and LB signals are active to select both

bytes. The obvious limitation to this method is that the

table write must be done in pairs on a specific word

boundary to correctly write a word location.

FIGURE 6-2:

16-BIT WORD WRITE MODE EXAMPLE

AD<7:0>

PIC18F8X2X

AD<15:8>

ALE

373

A<20:1>

373

WRH

A<19:16>

A<x:0>

D<15:0>

WR(1)

D<15:0>

JEDEC Word

EPROM Memory

Address Bus

Data Bus

Control Lines

Note

This signal only applies to table writes. See Section 5.1, “Table Reads and Writes”.

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