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M87C257-15C3TR Datasheet(PDF) 3 Page - STMicroelectronics |
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M87C257-15C3TR Datasheet(HTML) 3 Page - STMicroelectronics |
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3 / 13 page  Mode E GA9 ASVPP Q0 - Q7 Read (Latched Address) VIL VIL XVIL Data Out Read (Applied Address) VIL VIL XVIH Data Out Output Disable VIL VIH X X Hi-Z Program VIL Pulse VIH XVPP Data In Verify VIH VIL XVPP Data Out Program Inhibit VIH VIH XVPP Hi-Z Standby VIH X X X Hi-Z Electronic Signature VIL VIL VID VIL Codes Note: X = VIH or VIL, VID = 12V ± 0.5V Table 3. Operating Modes Identifier A0 Q7 Q6 Q5 Q4 Q3 Q2 Q1 Q0 Hex Data Manufacturer’s Code VIL 00100 00 0 20h Device Code VIH 10000 00 0 80h Table 4. Electronic Signature be used to gate data to the output pins, inde- pendent of device selection. Assuming that the addresses are stable (AS = VIH) or latched (AS = VIL), the address access time (tAVQV) is equal to the delay from E to output (tELQV). Data is available at the output after delay of tGLQV from the falling edge of G, assuming that E has been low and the ad- dresses have been stable for at least tAVQV-tGLQV. The M87C257 reduces the hardware interface in multiplexed address-data bus systems. The proc- essor multiplexed bus (AD0-AD7) may be tied to the M87C257’s address and data pins. No sepa- rate address latch is needed because the M87C257 latches all address inputs when AS is low. Standby Mode The M87C257 has a standby mode which reduces the active current from 30mA to 100 µA (Address Stable). The M87C257 is placed in the standby mode by applying a CMOS high signal to the E input. When in the standby mode, the outputs are in a high impedance state, independent of the G input. Two Line Output Control Because EPROMs are usually used in larger mem- ory arrays, this product features a 2 line control function which accommodates the use of multiple memory connection. The two line control function allows: a. the lowest possible memory power dissipation, b. complete assurance that output bus contention will not occur. For the most efficient use of these two control lines, E should be decoded and used as the primary device selecting function, while G should be made a common connection to all devices in the array and connected to the READ line from the system control bus. This ensures that all deselected mem- ory devices are in their low power standby mode and that the output pins are only active when data is desired from a particular memory device. 3/13 M87C257 |
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