ACE25C400 Datasheet, PDF (14/31 Pages) ACE Technology Co., LTD. – 4MB Serial Flash Memory

ACE25C400
4MB Serial Flash Memory
Fast Read (0Bh)
The Fast Read instruction is similar to the Read Data instruction except that it can operate at the
highest possible frequency of FR (see “12.6 AC Electrical Characteristics”). This is accomplished by
adding eight “dummy” clocks after the 24-bit address as shown in Figure 10. The dummy clocks allow
the devices internal circuits additional time for setting up the initial address. During the dummy clocks
the data value on the DO pin is a “don’t care”.
Figure 10 Fast read instruction
Fast Read Dual Output (3Bh)
The Fast Read Dual Output (3Bh) instruction is similar to the standard Fast Read (0Bh) instruction
except that data is output on two pins; DQ0 and DQ₁. This allows data to be transferred from the
ACE25C400 at twice the rate of standard SPI devices. The Fast Read Dual Output instru ction is ideal
for quickly downloading code from Flash to RAM upon power-up or for applications that cache
code-segments to RAM for execution.
Similar to the Fast Read instruction, the Fast Read Dual Output instruction can operate at the
highest possible frequency of FR (see “12.6 AC Electrical Characteristics”). This is accomplished by
adding eight “dummy” clocks after the 24-bit address as shown in Figure 11. The dummy clocks allow
the device's internal circuits additional time for setting up the initial address. The input data during the
dummy clocks is “don’t care”. However, the DQ₀ pin should be high-impedance prior to the falling
edge of the first data out clock.
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