memory products - Al Kossow's Bitsavers

ETC2732PROGRAM INHIBITProgramming multiple ETC2732s in parallel withdifferent data is also easily accQIDPlished. Exceptfor CE, all like inputs (including OE) of the parallelETC2732s may be common. A TIL level programI2Y!se applied to an ETC2732s CE input withOENl2I2...at 25 V will program that ETC2732. A highlevel CE input inhibits the other ETC2732s frombeing programmed.PROGRAM VERIFYA verify should be performed on the programmedbits to determine whether they were corre~ pro-9.@mmed. The verify is accomplished with OENppCE at VIL. Data should be verified tov after the faIlingedge of CEoERASURE CHARACTERISTICSThe erasure characteristics of the ETC2732 aresuch that erasure begins to oCCl:.lr when exposedto light with wavelenghts shorter than approximately4000 Angstroms (A). It should be noted thatsunlight and certain types of fluorescent lamps havewavelenghts in the 3000 A - 4000 A range. Datashows that constant exposure to room-levelfluorescent lighting could erase the typical ETC2732 in approximately 3 years, while it would takeapproximately 1 week to cause erasure when exposedto direct sunlight. If the ETC2732 is to beexposed to these types of lighting conditions forextended periods of time, opaque labels should beplaced over the ETC2732 window to prevent unin~tentional erasure. Covering the window will alsoprevent temporary functional failure due to the generationof photo currents.The recommended erasure procedure for the ETC2732 is exposure to shortwave ultraviolet lightwhich has a wavelength of 2537 Angstroms (A). Theintegrated dose (i.e., UV intensity x exposure time)for erasure should be a minimum of 15W-sec/cm2.The erasure time with this dosage is approximately21 minutes using an ultraviolet lamp with a 12,000p.W/cm2 power rating. The ETC2732 should be placewithin 1 inc/1 of the lamp tubes during erasure,Some lamps have a filter on their tubes whichshould be removed before erasure.An erasure system should be calibrated periodically.The distance from lamp to unit should be maintainedat one inch. The erasure time increases asthe square of the distance. (If distance is doubledthe erasure time increases by a factor of 4). Lampslose intensity as they age. When a lamp is changed,the distance has changed or the lamp hasaged, the system should be checked to make certainfull erasure is occurring. Incomplete erasurewill cause symptoms that can be misleading. Pr~grammers, components, and even system designshave been erroneously suspected when incompleteerasure was the problem.SYSTEM CONSIDERATIONThe power swhitching characiterics of EPROMs requirecareful decoupling of the devices. The supplycurrent, ICC, has three segments that are ofinterest to the system designer - the standby cUrrentlevel, the active current level, and the transientcurrent peaks that are produced on the falling andrising edges of chip enable. The magnitude of thesetransient current peaks is dependent on the outputcapacitance loading of the device. The associatedtransient voltgage peaks can be suppressedby properly selected decoupling capacitors. It is recommendedthat a 0.1p.F Ceramic capaCitor beused an every device between Vee and GND. Thisshould be a high frequency capacitor of low inherentinductance. In addition, a 4.7p.F.bulk electoly,tic capacitor should be used between Vee andGND. for each eight devices. The bulk capacitorshould be located near where the power supply isconnected to the array. The purpose of the bulkcapaCitor is to overcome the voltage drop causedby the inductive effects of the PC board traces.6110106