memory products - Al Kossow's Bitsavers

M27128ADEVICE OPERATION (Continued)The entire sequence of program pulses and byteverifications is performed at Vcc = 6V andVpp= 12.5V. When the Fast Programming cyclehas been completed, all bytes should be comparedto the original data with Vcc = Vpp = 5V.PROGRAM INHIBITProgramming of niultiple M27128As in parallel withdifferent data is also easily accq!!)plished. Exceptfor CE, all like inputs (including OE) of the parallelM27128A may be common. A TTL low pulse appliedto a M27128A's CEinput, with Vpp at 12.5V,will program that M27128A. A high level CE inputinhibits the other M27128A from beingprogrammed.PROGRAM VERIFYA verify should be performed on the programmedbits to determine that they were corre@programmed. The verify is accomplished with OEat V1L, CE at V1L, PGM at V1H and Vpp at 12.5V.ELECTRONIC 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 M27128A. To activate thismode, the programming equipment must force11.5V to 12.5V on address line A9 (pin 24) of theM27128A. Two identifier bytes may than be sequen-ced from the device outputs by toggling address lineAO (pin 10) from V1L to V1H. All other address linesmust be held at V1L during Electronic Signaturemode. Byte 0 (AO = V1J represents the manufacturercode and byte 1 (AO = V1H) the device identifiercode. For the SGS-THOMSON M27128A, thesetwo identifier bytes are given 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 M27128A 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 havewavelengths in the 3000-4000 A range. Data showsthat constant exposure to room level fluorescentlighting could erase a typical M27128A in about 3years, while it would take approximately 1 week tocause erasure when expose to direct sunlight. Ifthe M27128A is to be exposed to these types oflighting conditions for extended periods of time, itis suggested that opaque labels be put over theM27128A.window to prevent unintentional erasure.The recommended erasure procedure for theM27128A is exposure to short wave ultraviolet lightwhich has wavelength 2537 A. The integrated dose(i.e. UV intenSity x exposure time) for erasureshould be a minimum of 15 W-sec/cm2. Theerasure time with this dosage is approximately 15to 20 minutes using an ultraviolet lamp with 12000uW/cm2 power rating. The M27128A should beplaced within 2.5 cm (1 inch) of the lamp tubes duringthe erasure. Some lamps have a filter on theirtubes which should be removed before erasure.ELECTRONIC SIGNATURE MODE~ IDENTIFIERAO 07 06(10) (19) (18)MANUFACTURER CODE VIL 0 0DEVICE CODE VIH 1 005 04 03 02 01 00 Hex(17) (16) (15) (13) (12) (11) Data..1 0 0 0 0 0 200 0 1 0 0 1 896/1058