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M27256-20F1 Datasheet(PDF) 8 Page - STMicroelectronics |
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M27256-20F1 Datasheet(HTML) 8 Page - STMicroelectronics |
8 / 10 page VIH), and VPP = 12.5V. The outputs will be in a Hi-z state according to the signal presented to G. There- fore, all devices with VPP = 12.5V and G = VIL will present data on the bus independent of the E state. When parallel programming several devices which share the common bus, VPP should be lowered to VCC (6V) and the normal read mode used to exe- cute a program verify. Electronic Signature The Electronic Signature mode allows the reading out of a binary code from an EPROM that will identify its manufacturer and type. This mode is intended for use by programming equipment for the purpose of automatically matching the device to be programmed with its corresponding programming algorithm. This mode is functional in the 25 °C ± 5°C ambient temperature range that is required when programming the M27256. To activate this mode, the programming equipment must force 11.5V to 12.5V on address line A9 of the M27256. Two identifier bytes may then be sequenced from the device outputs by toggling address line A0 from VIL to VIH. All other address lines must be held at VIL during Electronic Signature mode. Byte 0 (A0 = VIL) represents the manufacturer code and byte 1 (A0 = VIH) the device identifier code. For the STMi- croelectronics M27256, these two identifier bytes are given below. ERASURE OPERATION (applies to UV EPROM) The erasure characteristic of the M27256 is such that erasure begins when the cells are exposed to light with wavelengths shorter than approximately 4000 Å. It should be noted that sunlight and some type of fluorescent lamps have wavelengths in the 3000-4000 Å range. Research shows that constant exposure to room level fluorescent lighting could erase a typical M27256 in about 3 years, while it would take approximately 1 week to cause erasure when exposed to direct sunlight. If the M27256 is to be exposed to these types of lighting conditions for extended periods of time, it is suggested that opaque lables be put over the M27256 window to prevent unintentional erasure. The recommended erasure procedure for the M27256 is exposure to short wave ultraviolet light which has wavelength 2537 Å. The integrated dose (i.e. UV intensity x exposure time) for erasure should be a minimum of 15 W-sec/cm2. The erasure time with this dosage is approximately 15 to 20 minutes using an ultra- violet lamp with 12000 µW/cm2 power rating. The M27256 should be placed within 2.5cm (1 inch) of the lamp tubes during the erasure. Some lamps have a filter on their tubes which should be re- moved before erasure. Speed and VCC Tolerance -1 170 ns, 5V ±5% -2 200 ns, 5V ±5% blank 250 ns, 5V ±5% -3 300 ns, 5V ±5% -4 400 ns, 5V ±5% -20 200 ns, 5V ±10% -25 250 ns, 5V ±10% Package F FDIP28W Temperature Range 1 0 to 70 °C 6 –40 to 85 °C Example: M27256 -1 F 1 ORDERING INFORMATION SCHEME For a list of available options (Speed, VCC Tolerance, Package, etc) refer to the current Memory Shortform catalogue. For further information on any aspect of this device, please contact STMicroelectronics Sales Office nearest to you. DEVICE OPERATION (cont’d) M27256 8/10 |
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