
DS89C430/DS89C440/DS89C450 Ultra-High-Speed Flash Microcontrollers 
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Table 11. Page Mode 2, Data Memory Cycle Stretch Values (PAGES1:PAGES0 = 11) 
RD/WR
 PULSE WIDTH (IN NUMBER OF OSCILLATOR CLOCKS) 
MD2:MD0 
STRETCH 
CYCLES 
4X/
CD0 = 100 
2X
, CD1, 
4X/
CD0 = 000 
2X
, CD1, 
4X/
CD0 = X10 
2X
, CD1, 
4X/
CD0 = X11 
2X
, CD1, 
000 
0 
0.5 
1 
2 
2048 
001 
1 
1 
2 
4 
4096 
010 
2 
2 
4 
8 
8192 
011 
3 
3 
6 
12 
12,288 
100 
7 
4 
8 
16 
16,384 
101 
8 
5 
10 
20 
20,480 
110 
9 
6 
12 
24 
24,576 
111 
10 
7 
14 
28 
28,672 
As shown in the previous tables, the stretch feature supports eight stretched external data-memory access options, 
which can be categorized into three timing groups. When the stretch value is cleared to 000b, there is no stretch on 
external data memory access, and a MOVX instruction is completed in two basic memory cycles. When the stretch 
value is set to 1, 2, or 3, the external data memory access is extended by 1, 2, or 3 stretch memory cycles, 
respectively. Note that the first stretch value does not result in adding four system clocks to the control signals. This 
is because the first stretch uses one system clock to create additional address setup and data bus float time and 
one system clock to create additional address and data hold time. When using very slow RAM and peripherals, a 
larger stretch value (4–7) can be selected. In this stretch category, two stretch cycles are used to create additional 
setup (the ALE pulse width is also stretched by one stretch cycle for page miss) and one stretch cycle is used to 
create additional hold time. The following timing diagrams illustrate the external data memory access at divide-by-1 
system clock mode (CD1:CD0 = 10b). 
Figure 12
 illustrates the external data-memory stretch-cycle timing relationship when PAGEE = 1 and 
PAGES1:PAGES0 = 01. The stretch cycle shown is for a stretch value of 1 and is coincident with a page miss. 
Note that the first stretch value does not result in adding four system clocks to the 
RD
/
WR
 control signals. This is 
because the first stretch uses one system clock to create additional setup and one system clock to create 
additional hold time. 
Figure 13
 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 a page miss. 
The stretched data memory bus cycle timing relationship for PAGES = 11 is identical to nonpage mode operation 
since the basic data memory cycle always contains four system clocks in this page mode operation.