CY27C256
5
Erasure Characteristics
Wavelengths of light less than 4000 Å begin to erase the
27C256 in the windowed package. For this reason, an opaque
label should be placed over the window if the EPROM is ex-
posed to sunlight or fluorescent lighting for extended periods
of time.
The recommended dose of ultraviolet light for erasure is a
wavelength of 2537 Å for a minimum dose (UV intensity mul-
tiplied by exposure time) of 25 Wsec/cm2. For an ultraviolet
lamp with a 12 mW/cm2 power rating, the exposure time would
be approximately 35 minutes. The CY27C256 needs to be
within 1 inch of the lamp during erasure. Permanent damage
may result if the EPROM is exposed to high-intensity UV light
for an extended period of time. 7258 Wsec/cm2 is the recom-
mended maximum dosage.
Programming Modes
Programming support is available from Cypress as well as
from a number of third-party software vendors. For detailed
programming information, including a listing of software pack-
ages, please see the EPROM Programming Information locat-
ed at the end of this section. Programming algorithms can be
obtained from any Cypress representative.
Switching Waveform
tOH
tPU
tPD
tAA
27c256–8
(tOE)
tACE
50%
50%
A0 -A14
ADDRESS
ICC
SUPPLY
CURRENT
OE,CE
O0 -O7 PREVIOUS DATA VALID
DATA VALID
POWER–DOWN CONTROLLED BY CE
(tHZOE)
tHZCE
HIGH Z
Table 1. CY27C256 Mode Selection.
Mode
Pin Function[8]
A14-A0
OE
CE
VPP
O7-O0
Read
A14-A0
VIL
VIL
X[9]
O7-O0
Output Disable
A14-A0
VIH
VIL
X
High Z
Power Down
A14-A0
X
VIH
X
High Z
Notes:
8.
X can be VIL or VIH
9.
VPP should not exceed VCC in read mode.