Материал: 271024

System Considerations

The power switching characteristics of Advanced CMOS 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 transient current peaks that are produced by the falling and rising edges of E. The magnitude of transient current peaks is dependent on the capacitive and inductive loading of the device at the output. The associated transient voltage peaks can be suppressed by complying with the two line output control and by properly selected decoupling capacitors. It is recommended that a 0.1μF ceramic capacitor be used on every device between VCC and VSS. This should be a high frequency capacitor of low inherent inductance and should be placed as close to the device as possible. In addition, a 4.7μF bulk electrolytic capacitor should be used betweenVcc and VSS for every eight devices.

The bulk capacitor should be located near the power supply connection point. The purpose of the bulk capacitor is to overcome the voltage drop caused by the inductive effects of PCB traces.

Programming

When delivered (and after each erasure for UV EPROM), all bits of the M27C1024 are in the º1º state. Data is introduced by selectively programming º0ºs into the desired bit locations. Although only º0ºs will be programmed, both º1ºs and º0ºs can be present in the data word. The only way to change a º0º to a º1º is by die exposureto ultraviolet light (UV EPROM). The M27C1024 is in the programming mode when VPP input is at 12.75V, and E and P are at TTL-low. The data to be programmed is applied, 16 bits in parallel, to the data output pins. The levels required for the address and data inputs are TTL. VCC is specified to be 6.25V ± 0.25V.

Figure 7. Programming Flowchart

YES

CHECK ALL WORDS 1st: VCC = 6V 2nd: VCC = 4.2V

AI00707B

PRESTO II Programming Algorithm

PRESTO II Programming Algorithm allows programming of the whole array with a guaranteed margin, in a typical time of 6.5 seconds. Programming with PRESTO II consists of applying a sequence of 100 μs programpulses to each word until a correct verify occurs (see Figure 7). During programming and verify operation, a MARGIN MODE circuit is automatically activated in order to guarantee that each cell is programmed with enough margin. No overprogram pulse is applied since the verify in MARGIN MODE provides necessary margin to each programmed cell.

Program Inhibit

Programming of multiple M27C1024s in parallel with different data is also easily accomplished. Except for E, all like inputs including G of the parallel M27C1024 may be common. A TTL low level pulse applied to a M27C1024's E input, with P low and VPP at 12.75V, will program that M27C1024. A high level E input inhibits the other M27C1024s from being programmed.

Program Verify

A verify (read) should be performed on the programmed bits to determine that they were correctly programmed. The verify is accomplished with E

and G at VIL, P at VIH, VPP at 12.75V and VCC at 6.25V.

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. This mode is functional in the 25°C ± 5°C ambient temperature range that is required when programming the M27C1024. To activate the ES mode, the programming equipmentmust force11.5V to 12.5V on address line A9 of the M27C1024 with VPP = VCC = 5V. 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 SGS-THOMSON M27C1024, these two iden-tifier bytes are given in Table 4 and can be read-out on outputs Q0 to Q7.

ORDERING INFORMATION SCHEME

ERASURE OPERATION (applies to UV EPROM)

The erasure characteristics of the M27C1024 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 M27C1024 in about 3 years, while it would take approximately 1 week to cause erasure when exposed to direct sunlight. If the M27C1024 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 M27C1024 window to prevent unintentional erasure. The recommended erasure procedure for the M27C1024 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 ultraviolet lamp with 12000 μW/cm2 power rating. The M27C1024 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 erasure.