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FM27C256V90 데이터시트(PDF) 8 Page - Fairchild Semiconductor |
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FM27C256V90 데이터시트(HTML) 8 Page - Fairchild Semiconductor |
8 / 10 page 8 www.fairchildsemi.com www.fairchildsemi.com FM27C256 Functional Description (Continued) ERASURE CHARACTERISTICS The erasure characteristics of the device are such that erasure begins to occur when exposed to light with wavelengths shorter than approximately 4000 Angstroms (Å). It should be noted that sunlight and certain types of fluorescent lamps have wavelengths in the 3000Å–4000Å range. The recommended erasure procedure for the EPROM is expo- sure to short wave ultraviolet light which has a wavelength of 2537Å. The integrated dose (i.e., UV intensity x exposure time) for erasure should be a minimum of 15W-sec/cm2. 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 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 distance 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 certain full erasure is occurring. Incomplete erasure will cause symptoms that can be misleading. Program- mers, components, and even system designs have been errone- ously 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 designer: the standby current level, the active current level, and the transient current peaks that are produced by voltage transitions on input pins. The magnitude of these transient current peaks is dependent of the output capacitance loading of the device. The associated V CC transient voltage peaks can be suppressed by properly selected decoupling capacitors. It is recommended that at least a 0.1 µF ceramic capacitor be used on every device between V CC and GND. This should be a high frequency capacitor of low inherent inductance. In addition, at least a 4.7 µF bulk electrolytic capacitor should be used between V CC and GND for each eight devices. The bulk capacitor should be located near where the power supply is connected to the array. The purpose of the bulk capacitor is to overcome the voltage drop caused by the inductive effects of the PC board traces. Mode Selection The modes of operation of FM27C256 listed in Table 1. A single 5V power supply is required in the read mode. All inputs are TTL levels except for V PP and A9 for device signature. TABLE 1. Modes Selection Pins CE/PGM OE VPP VCC Outputs Mode Read VIL VIL VCC 5.0V DOUT Output Disable X V IH V CC 5.0V High-Z (Note 16) Standby V IH XV CC 5.0V High-Z Programming V IL VIH 12.75V 6.25V D IN Program Verify V IH V IL 12.75V 6.25V D OUT Program Inhibit V IH V IH 12.75V 6.25V High-Z Note 16: X can be VIL or VIH. TABLE 2. Manufacturer’s Identification Code Pins A0 A9 O7O6O5O4O3O2O1O0 Hex (10) (24) (19) (18) (17) (16) (15) (13) (12) (11) Data Manufacturer Code V IL 12V 10001111 8F Device Code V IH 12V 00000100 04 |
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