Материал: 2764

Symbol Alt

tAVPL tAS

tQVPL tDS

tVPHPL tVPS

tVCHPL tVCS

tELPL tCES

tPLPH tPW

tPLPH tOPW

tPHQX tDH

tQXGL tOES

tGLQV tOE

(4)

tGHQZ tDFP

tGHAX tAH

Parameter

Address Valid to Program Low

Input Valid to Program Low

VPP High to Program Low

VCC High to Program Low

Chip Enable Low to Program Low

Program Pulse Width (Initial)

Program Pulse Width (Overprogram)

Program High to Input

Transition

Input Transition to Output Enable Low

Output Enable Low to Output Valid

Output Enable High to Output Hi-Z

Output Enable High to Address Transition

Figure 7. Fast Programming Flowchart

P = 3ms Pulse by n

FAIL

Last NO

Addr

YES

CHECK ALL BYTES

VCC = 5V, VPP 5V

AI00775B

DEVICE OPERATION (cont'd)

been successfully programmed. A flowchart of the M2764A Fast Programming Algorithm is shown on the last page. The Fast Programming Algorithm utilizes two different pulse types: initial and overprogram.

The duration of the initial P pulse(s) is 1ms, which will then be followed by a longer overprogrampulse of length 3ms by n (n is equal to the number of the initial one millisecond pulses applied to a particular M2764A location), before a correct verify occurs. Up to 25 one-millisecond pulses per byte are provided for before the overprogram pulse is applied.

The entire sequence of program pulses and byte verifications is performed at VCC = 6V and VPP = 12.5V.When the Fast Programming cycle has been completed, all bytes should be compared to the original data with VCC = 5V and VPP = 5V.

Program Inhibit

Programming of multiple M2764A in parallel with different data is also easily accomplished. Except for E, all like inputs (including G) of the parallel M2764A may be common. A TTL low pulse applied to a M2764A's E input, with VPP at 12.5V, will program that M2764A. A high level E input inhibits the other M2764As from being programmed.

Program Verify

A verify should be performed on the programmed bits to determine that they were correctly programmed. The verify is accomplished with G = VIL, E = VIL, P = VIH and VPP = 12.5V.

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 M2764A.

To activate this mode, the programming equipment must force 11.5V to 12.5V on address line A9 of the M2764A. 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 deviceidentifier code. For the SGS-THOMSON M2764A, these two identifier bytes are given below.

ERASURE OPERATION (applies to UV EPPROM)

The erasure characteristic of the M2764A 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 M2764A in about 3 years, while it would take approximately 1 week to cause erasure when exposed to direct sunlight. If the M2764A 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 M2764A window to prevent unintentional erasure. The recommended erasure procedure for the M2764A 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. Theerasure time with this dosage is approximately 15 to 20 minutes using an ultraviolet lamp with 12000 μW/cm2 power rating. The M2764A 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.