Материал: 274001

Symbol Alt

tAVEL tAS

tQVEL tDS

tVPHEL tVPS

tVCHEL tVCS

tELEH tPW

tEHQX tDH

tQXGL tOES

tGLQV tOE

tGHQZ tDFP

tGHAX tAH

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 the 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 between VCC 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 M27C4001 are in the º1º state. Data is introduced by selectively programming º0sº into the desired bit locations. Although only º0sº will be programmed, both º1sº and º0sº can be present in the data word. The only way to change a º0º to a º1º is by die exposition to ultraviolet light (UV EPROM). The M27C4001 is in the programming mode when VPP input is at 12.75V, and E is at TTL-low. The data to be programmed is applied 8 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.

M27C4001

Figure 7. Programming Flowchart

YES

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

AI00760B

PRESTO II Programming Algorithm

PRESTO II Programming Algorithm allows the whole array to be programmed with a guaranteed margin, in a typical time of 52.5 seconds. Programming with PRESTO II consists of applying a sequence of 100μs program pulses to each byte until a correct verify occurs. 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 the necessary margin to each programmed cell.

Program Inhibit

Programming of multiple M27C4001s in parallel with different data is also easily accomplished. Except for E, all like inputs including G of the parallel M27C4001 may be common. A TTL low level pulse applied to a M27C4001's E input, with VPP at 12.75V, will program that M27C4001. A high level E input inhibits the other M27C4001s 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 G at VIL , E at VIH, VPP at 12.75V and VCC at 6.25V.

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 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 M27C4001. To activate this mode, the programming equipmentmust force 11.5Vto 12.5V on address line A9 of the M27C4001 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 id en t ifie r co de . For th e S GS-THOMSO N M27C4001, these two identifier bytes are given in Table 4 and can be read-out on outputs Q0 to Q7.

ERASURE OPERATION (applies to UV EPROM)

The erasure characteristics of the M27C4001 are 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 3000-4000Å range. Data shows that constant exposure to room level fluorescent lighting could erase a typical M27C4001 in about 3 years, while it would take approximately 1 week to cause erasure when exposed to direct sunlight. If the M27C4001 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 M27C4001 window to prevent unintentional erasure. The recommended erasure procedure for the M27C4001 is exposure to short wave ultraviolet light which has wavelength of 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 M27C4001 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.