MEMORY DATABOOK - Al Kossow's Bitsavers

EPROM WRITING AND ERASURE1. EPROM WRITING ERASURE1.1 EPROM MSM2764 writingWriting in the MSM2764RS involves setting the drainand gate voltages of the floating gate stage to a highvoltage. When the cjrain voltage exceeds 15 V and thegate voltage 20 V, the channel charge (electrons) be·comes highly energized and flow over the oxide filmbarrier into the floating gate. And since the high gatevoltage is positive polarity, electrons will flow into thefloating gate very easily. When electron, build up inthe floating gate, the memory element "thresholdvoltage" is changed, and subsequently stored as memorydata. Once the charge has been built up, the surroundingoxide film (high insulation) prevents escape of electrons.The data is thus stored as "non·volatile" data.Drain1.2 PROM programmerOki Electric employs a system whereby the variousprogrammer available on the market are examined, andagreements reached with different programmer manufacturers.The purpose of this system is to checkcompatibility between programmer manufacturers andOki Electric devices, and making modifications wheneverrequired. Users are thus ensured trouble-free use.In the event of EPROM trouble with Oki devices andapproved programmer, problems will be handled byboth Oki and driver manufacturer except where suchproblems have been caused purposely.1.3 ErasureErasure of data written in the MSM2764RS canbe effected by ultra-violet radiation of the memoryelement. In this case, the charge is discharged into thesubstrate or electrode by the ultra-violet energy, butnote that the following erasure conditions must be met.If a memory which has not been properly erased is used,writing problems and operating failures are likely toarise. Also note that excessively long erasure times (ofseveral hours duration) can also result in failure.Gate0-----11 V!Floating GateCharging,..- Threshold--~~'-----When the MSM2764RS is shipped from the factory,the floating gate is left in discharged status (all bits "1"),i.e. "blank" status. During writing processes, +25 V isapplied to the Vpp terminal and VIH to the OE input.The data to be programmed is applied in parallel to theoutputs (0. -7). After the address and data have beenset up, application of VIH level for 50ms to the CEinput will enable writing of data. Since the +25 Vapplied to Vpp is fairly close to the element's with·standing voltage, make sure that the voltage setting ismaintained strictly within the 25 V ± 1 V range. Applica·tion of voltages in excess of the rated VOltage, andoversh"oting, to the Vpp terminal can result in permanentdamage to the element.Although MSM2764RS rewriting should be checkedabout 100 times by sample testing, in actual practice 5to 10 times is usually the limit. This will not likelyresult in any problem.Exposure timeLengthy exposure to direct sunlight can also resultin loss of bits. Direct exposure of MSM2764 tothe strong summer sun for a single day can result in bitchanges. Although normal fluorescent lights havepractically no effect, light rays beamed onto elementscan cause special changes. I t is therefore recommendedthat the glass face be covered with a screening label.39