Rainbow Electronics W27E520 User Manual

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Advance Information W27E520

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FUNCTIONAL DESCRIPTION

Read Mode

Unlike conventional UVEPROMs, which has CE and OE two control functions, the W27E520 has one

OE /V

and one ALE (address_latch_enable) control functions. The ALE makes lower address A[7:0]

to be latched in the chip when it goes from high to low, so that the same bus can be used to output
data during read mode. i.e. lower address A[7:0] and data bus DQ[7:0] are multiplexed. OE /V

controls the output buffer to gate data to the output pins. When addresses are stable, the address
access time (T

ACC

) is equal to the delay from ALE to output (T

), and data are available at the

outputs T

after the falling edge of OE /V

, if T

ACC

and T

timings are met.

Erase Mode

The erase operation is the only way to change data from "0" to "1." Unlike conventional UVEPROMs,
which use ultraviolet light to erase the contents of the entire chip (a procedure that requires up to half
an hour), the W27E520 uses electrical erasure. Generally, the chip can be erased within 100 mS by
using an EPROM writer with a special erase algorithm.
There are two ways to enter Erase mode. One is to raise OE /V

to V

(13V), V

= V

(6.5V), A9

= V

(13V), A10 = high A8&A11 = low, and all other address pins include AD[7:0] keep at fixed low

or high. Pulsing ALE high starts the erase operation. The other way is somewhat like flash, by
programming two consecutive commands into the device and then enter Erase mode. The two
commands are loading Data = AA(hex) to Addr. = 5555(hex) and Data = 10(hex) to Addr. =
2AAA(hex). Be careful to note that the ALE pulse widths of these two commands are different: One is
50uS, while the other is 100mS. Please refer to the Smart Erase Algorithm 1 & 2.

Erase Verify Mode

The device will enter the Erase Verify Mode automatically after Erase Mode. Only power down the
device can force the device enter Normal Read Mode again.

Program Mode

Programming is the only way to change cell data from "1" to "0." The program mode is entered when

OE /V

is raised to V

(13V), V

= V

(6.5V), the address pins equal the desired addresses, and

the input pins equal the desired inputs. Pulsing ALE high starts the programming operation.

Program Verify Mode

The device will enter the Program Verify Mode automatically after Program Mode. Only power down
the device can force the device enter Normal Read Mode again.

Erase/Program Inhibit

Erase or program inhibit mode allows parallel erasing or programming of multiple chips with different
data. When ALE low, erasing or programming of non-target chips is inhibited, so that except for the
ALE and OE /V

pins, the W27E520 may have common inputs.

Standby Mode

The standby mode significantly reduces V

current. This mode is entered when ALE and OE /V

keep high. In standby mode, all outputs are in a high impedance state.

System Considerations