DS89C420-QCL Datasheet, PDF (73/139 Pages) Maxim Integrated Products – Ultra-High-Speed Flash Microcontroller User’s Guide

Ultra-High-Speed Flash
Microcontroller User’s Guide
PAGE MODE 1 DATA MEMORY TIMING–PAGES 1:0 = 01b (TWO CYCLES) (CONTINUED)
The first diagram below shows execution of a MOVX instruction with default stretch value = 1 (MD2:0 = 001b) from external program
memory. The most probable case, where a page-miss is needed for the MOVX instruction, is given here. However, if the MOVX address
happened to coincide with the current code execution page, a page hit would occur.
The second diagram illustrates the MOVX timing that would occur if the address MSB for the MOVX data were to coincide with the
code execution pages before and after the data access. Since a different MSB would not need to be latched, neither of the page-miss
cycles seen in the third diagram would occur.
TWO-CYCLE PAGE MODE 1: MOVX (THREE CYCLE) EXTERNAL CODE EXECUTION WITH PAGE MISSES
SYSCLK
ALE
PSEN
WR / RD
PORT2
LSB
PORT0
LSB
MOVX
MSB
MOVX
LSB
MOVX
DATA
MSB
LSB
MOVX
INST
(Page Hit)
MOVX
Data Access
(Page Miss + 1 Stretch Cycle)
INST
(Page Miss)
TWO-CYCLE PAGE MODE 1: MOVX (THREE CYCLE) EXTERNAL CODE EXECUTION - NO PAGE MISSES
SYSCLK
ALE
PSEN
WR / _RD
PORT2
LSB
PORT0
MOVX
#1
LSB
INST
(Page Hit)
= STRETCH CYCLE
MOVX
LSB
MOVX
DATA
MOVX
Data Access
(Page Hit + 1 Stretch Cycle)
LSB
LSB
LSB
INST
(Page Hit)
INST
(Page Hit)
INST
(Page Hit)
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