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M27V256-200N6TR Datasheet(PDF) 9 Page - STMicroelectronics |
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M27V256-200N6TR Datasheet(HTML) 9 Page - STMicroelectronics |
9 / 15 page 9/15 M27V256 On-Board Programming The M27V256 can be directly programmed in the application circuit. See the relevant Application Note AN620. Electronic Signature The Electronic Signature (ES) 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 to automatically match the device to be programmed with its corresponding programming algorithm. The ES mode is functional in the 25 °C ± 5°C am- bient temperature range that is required when pro- gramming the M27V256. To activate the ES mode, the programming equipment must force 11.5V to 12.5V on address line A9 of the M27V256, with VCC =VPP = 5V. Two identifier bytes may then be sequenced from the device outputs by toggling ad- dress line A0 from VIL to VIH. All other address lines must be held at VIL during Electronic Signa- ture mode. Byte 0 (A0=VIL) represents the manu- facturer code and byte 1 (A0=VIH) the device identifier code. For the STMicroelectronics M27V256, these two identifier bytes are given in Table 4 and can be read-out on outputs Q0 to Q7. Note that the M27V256 and M27C256B have the same identifier bytes. ERASURE OPERATION (applies for UV EPROM) The erasure characteristics of the M27V256 is such that erasure begins when the cells are ex- posed to light with wavelengths shorter than ap- proximately 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 fluo- rescent lighting could erase a typical M27V256 in about 3 years, while it would take approximately 1 week to cause erasure when exposed to direct sunlight. If the M27V256 is to be exposed to these types of lighting conditions for extended periods of time, it is suggested that opaque labels be put over the M27V256 window to prevent unintentional era- sure. The recommended erasure procedure for the M27V256 is exposure to short wave ultraviolet light which has wavelength 2537Å. The integrated dose (i.e. UV intensity x exposure time) for erasure should be a minimum of 15 W-sec/cm 2. The era- sure time with this dosage is approximately 15 to 20 minutes using an ultraviolet lamp with 12000 µW/cm2 power rating. The M27V256 should be placed within 2.5 cm (1 inch) of the lamp tubes during the erasure. Some lamps have a filter on their tubes which should be removed before era- sure. |
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