TMS27C040 524288 BY 8BIT UV ERASABLE

TMS27PC040 524288 BY 8BIT

PROGRAMMABLE READONLY MEMORY

SMLS040F − NOVEMBER 1990 − REVISED SEPTEMBER 1997

3

POST OFFICE BOX 1443

power down

100

µA by applying a high CMOS input on E. In this mode all outputs are in the high-impedance state.

erasure ( TMS27C040)

Before programming, the TMS27C040 EPROM is erased by exposing the chip through the transparent lid to

a high intensity UV-light (wavelength 2537 Å). The recommended minimum exposure dose (UV intensity

×

exposure time) is 15-W

lamp must be located about 2.5 cm above the chip during erasure. After erasure, all bits are in the high state.

Normal ambient light contains the correct wavelength for erasure; therefore, when using the TMS27C040, the

window must be covered with an opaque label. After erasure (all bits in logic high state), logic lows are

programmed into the desired locations. A programmed low can be erased only by UV light.

initializing ( TMS27PC040)

The OTP TMS27PC040 PROM is provided with all bits in logic high state, then logic lows are programmed into

the desired locations. Logic lows programmed into an OTP PROM cannot be erased.

SNAP! Pulse programming

The TMS27C040 and TMS27PC040 are programmed by using the SNAP! Pulse programming algorithm. The

programming sequence is shown in the SNAP! Pulse programming flow chart shown in Figure 1.

is presented in parallel (eight bits) on pins DQ0 through DQ7. Once addresses and data are stable, the

programmed only once before going to interactive mode.

verification and programming is performed up to a maximum of 10 times. When the device is fully programmed,

program inhibit

Programming can be inhibited by maintaining high level inputs on the E and G pins.

program verify

signature mode

The signature mode provides access to a binary code identifying the manufacturer and type. This mode is

activated when A9 (pin 26) is forced to 12 V. Two identifier bytes are accessed by toggling A0. All other

addresses must be held low. The signature code for the TMS27C040 is 9750. A0 low selects the manufacturer’s

code 97 (Hex), and A0 high selects the device code 50 (Hex), as shown in Table 3.

Table 3. Signature Mode

IDENTIFIER†

PINS

IDENTIFIER†

A0

DQ7

DQ6

DQ5

DQ4

DQ3

DQ2

DQ1

DQ0

HEX

MANUFACTURER CODE

VIL

1

0

0

1

0

1

1

1

97

DEVICE CODE

VIH

0

1

0

1

0

0

0

0

50

† E = G = VIL, A1-A8 = VIL, A9 = VH, A10-A18 = VIL, VPP = VCC.