DS89C420-ENL MAXIM [Maxim Integrated Products], DS89C420-ENL Datasheet - Page 28

• Manufacturer Part Number: DS89C420-ENL
• Description: Ultra-High-Speed Microcontroller
• Manufacturer: MAXIM [Maxim Integrated Products]

Figure 7. PAGE MODE 2, EXTERNAL CODE FETCH CYCLE (CD1:CD0 = 10)
STRETCH EXTERNAL DATA MEMORY CYCLE IN PAGE MODE
The DS89C420 allows software to adjust the speed of external data memory access by stretching the
memory bus cycle in page mode operation just like non-page mode operation. The following tables
summarize the stretch values and their effects on the external MOVX- memory bus cycle and the control
signals’ pulse width in terms of the number of oscillator clocks. A stretch machine cycle always contains
four system clocks, independent of the logic value of the page mode select bits.
Table 8. PAGE MODE 1, DATA MEMORY CYCLE STRETCH VALUES
(PAGES1:PAGES0 = 00)
MD2:MD0
XTAL1
PSEN
Port 0
Port 2
ALE
000
001
010
011
100
101
110
111
Internal Memory Cycles
STRETCH
CYCLES
10
0
1
2
3
7
8
9
RD / WR PULSE WIDTH (IN NUMBER OF OSCILLATOR CLOCKS)
4X/2X, CD1,
CD0 = 100
0.25
0.75
1.75
2.75
3.75
4.75
5.75
6.75
C1
28 of 58
4X/2X, CD1,
MSB Add
CD0 = 000
C2
Page Miss
11.5
13.5
0.5
1.5
3.5
5.5
7.5
9.5
LSB Add
C3
Ext Code Fetches
C4
Data
4X/2X, CD1,
CD0 = X10
C1
11
15
19
23
27
Page Hit
1
3
7
LSB Add
C2
Data
C1 C2
4X/2X, CD1,
CD0 = X11
Page Hit
11,264
15,360
19,456
23,552
27,648
1024
3072
7168
LSB Add
Data
DS89C420