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AMD27C64-255DC Datasheet(PDF) 5 Page - Advanced Micro Devices |
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AMD27C64-255DC Datasheet(HTML) 5 Page - Advanced Micro Devices |
5 / 11 page AMD 2-14 Am27C64 FUNCTIONAL DESCRIPTION Erasing the Am27C64 In order to clear all locations of their programmed con- tents, it is necessary to expose the Am27C64 to an ultraviolet light source. A dosage of 15 W seconds/cm2 is required to completely erase an Am27C64. This dosage can be obtained by exposure to an ultraviolet lamp— wavelength of 2537 A °—with intensity of 12,000 µW/cm2 for 15 to 20 minutes. The Am27C64 should be directly under and about one inch from the source and all filters should be removed from the UV light source prior to erasure. It is important to note that the Am27C64 and similar devices will erase with light sources having wavelengths shorter than 4000 A °. Although erasure times will be much longer than with UV sources at 2537 A °, exposure to fluorescent light and sunlight will eventually erase the Am27C64 and exposure to them should be prevented to realize maximum system reliability. If used in such an environment, the package window should be covered by an opaque label or substance. Programming the Am27C64 Upon delivery or after each erasure the Am27C64 has all 65,536 bits in the “ONE” or HIGH state. “ZEROs” are loaded into the Am27C64 through the procedure of programming. The programming mode is entered when 12.75 V ± 0.25 V is applied to the VPP pin, CE is at VIL and PGM is at VIL. For programming, the data to be programmed is applied 8 bits in parallel to the data output pins. The Flashrite algorithm reduces programming time by using 100 µs programming pulses and by giving each address only as many pulses as is necessary in order to reliably program the data. After each pulse is applied to a given address, the data in that address is verified. If the data does not verify, additional pulses are given until it verifies or the maximum is reached. This process is repeated while sequencing through each address of the Am27C64. This part of the algorithm is done at VCC = 6.25 V to assure that each EPROM bit is pro- grammed to a sufficiently high threshold voltage. After the final address is completed, the entire EPROM mem- ory is verified at VCC = VPP = 5.25 V. Please refer to Section 6 for programming flow chart and characteristics. Program Inhibit Programming of multiple Am27C64 in parallel with dif- ferent data is also easily accomplished. Except for CE, all like inputs of the parallel Am27C64 may be common. A TTL low-level program pulse applied to an Am27C64 PGM input with VPP = 12.75 V ± 0.25 V and CE Low will program that Am27C64. A high-level CE input inhibits the other Am27C64 devices from being programmed. Program Verify A verify should be performed on the programmed bits to determine that they were correctly programmed. The verify should be performed with OE and CE at VIL , PGM at VIH, and VPP between 12.5 V and 13.0 V. Auto Select Mode The auto select 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 Am27C64. To activate this mode, the programming equipment must force 12.0 V ± 0.5 V on address line A9 of the Am27C64. 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 dur- ing auto select mode. Byte 0 (A0 = VIL) represents the manufacturer code, and byte 1 (A0 = VIH), the device code. For the Am27C64, these two identifier bytes are given in the Mode Select Table. All identifiers for manufacturer and device codes will possess odd parity, with the MSB (DQ7) defined as the parity bit. Read Mode The Am27C64 has two control functions, both of which must be logically satisfied in order to obtain data at the outputs. Chip Enable ( CE) is the power control and should be used for device selection. Output Enable ( OE) is the output control and should be used to gate data to the output pins, independent of device selection. As- suming that addresses are stable, address access time (tACC) is equal to the delay from CE to output (tCE). Data is available at the outputs tOE after the falling edge of OE, assuming that CE has been LOW and addresses have been stable for at least tACC–tOE. Standby Mode The Am27C64 has a CMOS standby mode which re- duces the maximum VCC current to 100 µA. It is placed in CMOS-standby when CE is at VCC ± 0.3 V. The Am27C64 also has a TTL-standby mode which reduces the maximum VCC current to 1.0 mA. It is placed in TTL-standby when CE is at VIH. When in standby mode, the outputs are in a high-impedance state, independent of the OE input. |
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