ST9040 datasheet(42/56 Pages) STMICROELECTRONICS

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1.1 MEMORY

The memory of the ST90E40 is functionallydivided

into two areas, the Register File and Memory. The

Memory is divided into two spaces, each having a

maximum of 65,536 bytes. The two memory

spaces are separated by function, one space for

Program code, the other for Data. The ST90E40

16K bytes of on-chip EPROM memory are se-

lected at memory addresses 0 through 3FFFh

(hexadecimal) in the PROGRAM space, while the

ST90T40 OTP version has the top 64 bytes of the

EPROM reserved by SGS-THOMSON for testing

purposes. The DATA space includes the 512 bytes

of on-chip EEPROM at addresses 0 through 1FFh

and the 256 bytes of on-chip RAM memory at

memory addresses 200h through 2FFh.

WARNING. The ST90T40 has its 64 upper bytes in

the internal EPROM reserved for testing purpose.

External memory may be addressed using the mul-

tiplexed address and data buses (Alternate Func-

tions of Ports 0 and 1). At addresses greater than

the first 16K of program space, the ST90E40 exe-

cutes external memory cycles for instruction

fetches. Additional Data Memory may be decoded

externally by using the P/D Alternate Function out-

put. The on-chip general purpose (GP) Registers

may also be used as RAM memory for minimum

chip count systems.

1.2 EPROM PROGRAMMING

The 16384 bytes of EPROM memory of the

ST90E40 (16320 for the ST90T40) may be pro-

grammed by using the EPROM Programming

Boards (EPB) available from SGS-THOMSON.

1.2.1 Eprom Erasing

The EPROM of the windowed package of the

ST90E40may be erased by exposureto Ultra-Violet

light.

The erasure characteristic of the ST90E40 is such

that erasure begins when the memory is exposed

to light with a wave lengths shorter than approxi-

mately 4000Å. It should be noted that sunlight and

some types of fluorescent lamps have wave-

lengths in the range 3000-4000Å. It is thus recom-

mended that the

window of the ST90E40

packages be covered by an opaque label to pre-

vent unintentional erasure problems when testing

the application in such an environment.

The recommended erasure procedure of the

EPROM is the exposure to short wave ultraviolet

light which have a wave-length 2537Å. The inte-

grated dose (i.e. U.V. intensity x exposuretime) for

erasure should be a minimum of 15W-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 ST90E40 should

be placed within 2.5cm (1Inch) of the lamp tubes

during erasure.

Figure 4. Memory Spaces

ST90E40 - ST90T40

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