DS89C420 Dallas Semiconducotr, DS89C420 Datasheet - Page 32

• Manufacturer Part Number: DS89C420
• Description: Ultra-High-Speed Microcontroller
• Manufacturer: Dallas Semiconducotr

Figure 10. Page Mode 1, External Data Memory Access (Pages = 01,
Stretch = 4, CD = 10)
Figure 10 shows the timing relationship for a slow peripheral interface (stretch value = 4). Note that a
page hit data-memory cycle is shorter than a page miss data-memory cycle. The ALE pulse width is also
stretched by a stretch cycle in the case of page miss.
The stretched data-memory bus-cycle timing relationship for PAGES = 11 is identical to non-page mode
operation since the basic data-memory cycle always contains four system clocks in this page mode
operation.
RD / WR
RD / WR
XTAL1
PSEN
Port 0
Port 2
PSEN
Port 0
Port 2
ALE
ALE
LSB LSB
LSB
Inst
Inst
Instruction
Instruction
LSB
Inst
MOVX
Inst
MOVX
Fetch
Fetch
LSB
LSB
Inst
Inst
Cycle
Cycle
LSB
LSB
1st
1st
Inst
Inst
Cycle
2nd
Cycle
2nd
MSB
Cycle
3rd
Cycle
3rd
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MOVX Instruction (Page miss)
MOVX Instruction (Page hit)
Memory Access (Stretch = 4)
Memory Access (Stretch = 4)
Cycle
4th
Cycle
4th
Cycle
5th
Cycle
Data
LSB
9th
Data
LSB
Cycle
9th
LSB LSB LSB
Inst
LSB LSB
Inst
Inst
Inst
Inst