DS89C420-QCL Datasheet, PDF (75/139 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 = 00b (ONE CYCLE) (CONTINUED)
The next diagram, still using a MOVX stretch value = 0, shows the back-to-back MOVX instructions being executed from external pro-
gram memory.
The last diagram shows external code memory execution of an external MOVX instruction with stretch value = 4 (MD2:0 = 100b). It has
been assumed, for this example, that a page-miss is required for the MOVX data access. A stretch value = 4 results in the addition of
4 stretch cycles beyond the stretch value = 3. The four stretch cycles are distributed as folllows: two stretch cycles added for address
setup, one stretch cycle added to RD or WR pulse duration, and 1 stretch cycle added for address/data hold. For subsequent stretch
values of 5, 6, or 7, the added stretch cycle increases the RD or WR pulse duration.
ONE-CYCLE PAGE MODE 1: MOVX (TWO CYCLES) — MOVX (TWO CYCLES) EXTERNAL CODE EXECUTION
SYSCLK
ALE
PSEN
WR / _RD
PORT2
PORT0
LSB
LSB
MOVX MOVX
MSB LSB
MSB
LSB
MOVX MOVX _MSB
MSB LSB
LSB
LSB
LSB
LSB
LSB
LSB
LSB
MOVX
DATA
MOVX
DATA
MOVX MOVX
#1 #2
MOVX #1
Data Access
(Page Miss)
INST
(Page Miss)
MOVX #2
Data Access
(Page Miss)
INST
(Page Miss)
INSTRUCTIONS
ONE-CYCLE PAGE MODE 1: MOVX (NINE CYCLES) EXTERNAL CODE EXECUTION
SYSCLK
ALE
PSEN
WR / _RD
PORT2
LSB LSB
Stretch #1
MOVX MSB
Stretch #2
Stretches #3-6
MOVX LSB
Stretch #7
PORT0
MOVX DATA
MOVX INST
MOVX Data Access
(Page Miss + 7 Stretch Cycles)
MSB LSB
INST
(Page Miss)
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