DM163006 datasheet(82/320 Pages) MICROCHIP

82 / 320 page

PIC18C601/801

DS39541A-page 82

Advance Information

 2001 Microchip Technology Inc.

6.3.4

16-BIT EXTERNAL TABLE WRITE

(BYTE SELECT MODE)

This mode allows Table Writes to word-wide external

memories that have byte selection capabilities. This

generally includes word-wide FLASH devices and

word-wide static RAM devices.

During a TBLWT cycle, the TABLAT data is presented

on the upper and lower byte of the AD<15:0> bus.

The WRH line is strobed for each write cycle and the

WRL line is unused. The BA0 or UB or UL lines are

used to select the byte to be written, based on the LSb

of the TBLPTR.

JEDEC standard flash memories will require a I/O port

line to become a BYTE/WORD input signal and will

use the BA0 signal as a byte address. JEDEC stan-

dard static RAM memories will use the UB or UL sig-

nals to select the byte.

Figure 6-10 shows the timing associated with this mode.

FIGURE 6-10:

TBLWT

EXTERNAL INTERFACE TIMING (16-BIT BYTE SELECT MODE)

Q3 Q4

ALE

WRH

WRL

BA0

Opcode Fetch

TBLWT*+

TBLWT* Cycle1

MOVLW 55h

from 007554h

Q3 Q4

TBLWT 56h

to 199E66h

from 00755Ah

Memory

Cycle

Instruction

Execution

INST(PC-2)

TBLWT* Cycle2

MOVWF TABLAT

from 007556h

Q3 Q4

TBLWT 92h

to 199E67h

TBLWT*+ Cycle1 TBLWT*+ Cycle2

Opcode Fetch

TBLWT*

from 007558h

MOVWF

’1’

A<19:16>

3AAAh

AD<15:0>

000Dh

CF33h

5656h

3AABh

6FF4h

3AACh

000Ch

3AADh

0E55h

CF33h

9292h

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