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NM27C256N150 Datasheet(PDF) 8 Page - National Semiconductor (TI) |
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NM27C256N150 Datasheet(HTML) 8 Page - National Semiconductor (TI) |
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8 / 12 page  Functional Description (Continued) Program Verify A verify should be performed on the programmed bits to determine whether they were correctly programmed The verify may be performed with VPP at 1275V VPP must be at VCC except during programming and program verify AFTER PROGRAMMING Opaque labels should be placed over the EPROM window to prevent unintentional erasure Covering the window will also prevent temporary functional failure due to the genera- tion of photo currents MANUFACTURER’S IDENTIFICATION CODE The EPROM has a manufacturer’s identification code to aid in programming When the device is inserted in an EPROM programmer socket the programmer reads the code and then automatically calls up the specific programming algo- rithm for the part This automatic programming control is only possible with programmers which have the capability of reading the code The Manufacturer’s Identification code shown in Table II specifically identifies the manufacturer and device type The code for NM27C256 is ‘‘8F04’’ where ‘‘8F’’ designates that it is made by National Semiconductor and ‘‘04’’ designates a 256K part The code is accessed by applying 12V g05V to address pin A9 Addresses A1 – A8 A10 – A16 and all control pins are held at VIL Address pin A0 is held at VIL for the manu- facturer’s code and held at VIH for the device code The code is read on the eight data pins O0–O7 Proper code access is only guaranteed at 25 Cto g5 C ERASURE CHARACTERISTICS The erasure characteristics of the device are such that era- sure begins to occur when exposed to light with wave- lengths shorter than approximately 4000 Angstroms ( ) It should be noted that sunlight and certain types of fluores- cent lamps have wavelengths in the 3000 – 4000 range The recommended erasure procedure for the EPROM is ex- posure to short wave ultraviolet light which has a wave- length of 2537 The integrated dose (ie UV intensity c exposure time) for erasure should be a minimum of 15W-seccm2 The EPROM should be placed within 1 inch of the lamp tubes during erasure Some lamps have a filter on their tubes which should be removed before erasure Table III shows the minimum EPROM erasure time for various light intensities An erasure system should be calibrated periodically The distance from lamp to device should be maintained at one inch The erasure time increases as the square of the dis- tance from the lamp (if distance is doubled the erasure time increases by factor of 4) Lamps lose intensity as they age When a lamp is changed the distance has changed or the lamp has aged the system should be checked to make cer- tain full erasure is occurring Incomplete erasure will cause symptoms that can be misleading Programmers compo- nents and even system designs have been erroneously suspected when incomplete erasure was the problem SYSTEM CONSIDERATION The power switching characteristics of EPROMs require careful decoupling of the devices The supply current ICC has three segments that are of interest to the system de- signer the standby current level the active current level and the transient current peaks that are produced by volt- age transitions on input pins The magnitude of these tran- sient current peaks is dependent of the output capacitance loading of the device The associated VCC transient voltage peaks can be suppressed by properly selected decoupling capacitors It is recommended that at least a 01 mF ceramic capacitor be used on every device between VCC and GND This should be a high frequency capacitor of low inherent inductance In addition at least a 47 mF bulk electrolytic capacitor should be used between VCC and GND for each eight devices The bulk capacitor should be located near where the power supply is connected to the array The pur- pose of the bulk capacitor is to overcome the voltage drop caused by the inductive effects of the PC board traces 8 |
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Similar Description - NM27C256N150 |
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