memory products - Al Kossow's Bitsavers

M27512DEVICES OPERATION (Continued)PROGRAM INHIBITProgramming of multiple M27512s in parallel withdifferent data is also easily accQIDPlished. Exceptfor~, all like inputs (including OENpp) of the parallelM27512 may be common. A TTL low level pulseapplied to a M27512's ~ input, with OENppat 12.5V, will program that M27512. A high level~input inhibits the other M27512s from being programmed.PROGRAM VERIFYA verify (read) should be performed on the programmedbits to determine that they were corre~ programmed.The verify is accomplished with OENppand CE at VIL. Data should be verified tov after thefalling edge of CEoELECTRONIC SIGNATUREThe Electronic Signature mode allows the readingout of a binary code from an EPROM that will identifyits manufacturer and type. This mode is intendedfor use by programming equipment for thepurpose of automatically matching the device tobe programmed with its corresponding programmingalgorithm. This mode is functional in the 25°C±5°C ambient temperature range that is requiredwhen programming the M27512. To activate thismode, the programming equipment must force11.5V to 12.5V on address line A9 (pin 24) of theM27512. Two identifier bytes may then be sequencedfrom the device outputs by toggling addressline AO (pin 10) from VIL to VIH. All other addresslines must be held at VIL during Electronic Signa-ture mode, except for A14 and A15 which shouldbe held high. Byte 0 (AO = VILl represents the manufacturercode and byte 1 (AO = VI H) the deviceidentifier code. For the SGS M27512, these twoidentifier bytes are given here below. All identifiersfor manufacturer and device codes will possess oddparity, with the MSB (07) defined as the parity bit.ERASURE OPERATIONThe erasure characteristic of the M27512 is suchthat erasure begins when the cells are exposed tolight with wavelengths shorter than approximately4000 Angstrom A.. It should be noted that sunlightand some type of fluorescent lamps have wavelengthsin the 3000-4000 A range. Data shows thatconstant exposure to room level fluorescent lightingcould erase a typical M27512 in about 3 years,while it would take approximately 1 week to causeerasure when expose to direct sunlight. If theM27512 is to be exposed to these types of lightingconditions for extended periods of time, it is suggestedthat opaque labels be put over the M27512window to prevent unintentional erasure. The recommendederasure procedure for the M27512 isexposure to short wave ultraviolet light which haswavelength 2537 A.. The integrated dose (Le. UVintensity x exposure time) for erasure should be aminimum of 15 W-sec/cm2• The erasure time withthis dosage is approximately 15 to 20 minutes usingan ultraviolet lamp with 12000 uW/cm2 power rating.The M27512 should be placed within 2.5 cm(1 inch) of the lamp tubes during the erasure. SQmelamps have a filter on their tubes which shouldbe removed before erasure.ELECTRONIC SIGNATURE MODE~sIDENTIFIERAO 07 06(10) (19) (18)MANUFACTURER CODE VIL 0 0DEVICE CODE VIH 0 005 04 03 02 01 00 Hex(17) (16) (15) (13) (12) (11) Data1 0 0 0 0 0 200 0 1 1 0 1 00Noie: A9=12V :O.S\(; A1·AB, Al0·A13, CE, OENpp=V,L; A14, A1S=V,H9/1581