Testing of ROM.

Functional faults:1. Main SAF;2. Amplifier SAF;3. R/W line SAF;4. Selection CS SAF;5. Data line SAF;6. Data line interruption;7. Data line short-circuit;8. Data line cross-talk;9. Address line SAF;10. Address line interruption;11. Address line short-circuit;12. Interruption in decoder;13. Selection of the wrong address;14. Turning to several addresses;15. Faults in transition (0 to 1and vice versa);16. Dependence of data between slots.

Classification of faults:1. SAF stuck at 0/1 faults 1-6;2. CF coupling faults faults 7,8 and 16;3. TF transition faults fault 15;4. AF address decoder faults faults 9-14.

Faults in ROMs and their classification

Constant faults:1. Connection faults;2. Broken components;3. Faults in manufacturing;4. Faults in design.

Unstable faults:1. Environment (temp. humidity, pressure ...);2. Vibration;3. Feed;4. Electromagnetic field, static electricity, ground;5. Bad connections;6. Timing;7. Changes in resistance and capacity,8. Noise;9. Ageing.

Possible causes of faults in ROMs.

DC

A0

A 3

1 1

0

1

2

3

b1 b2

Programmable ROM

DC

A0

A 3

0

1

2

3

+v +v

b1 b2

1

1

1

1

0

0

0

1

1

1

0 1

Fuse

Mask-programmed ROM

DC

A0

A 3

0

1

2

3

+v +v

b1 b2

1

1

1

1

0

0

0

1

1

1

tension 2U1

tension U1

tension U1

tension U1

tension 0

tension 0

The only fuse that falls under thevoltage of 2U resulting in its melting.

Programming of EPROM

p

n n

Silicon floating gate

Silicon fixed gateVss Vdd

Vgg

EPROM array

Vdd Vdd

VddVdd

WLi

Wli+1

BLi Bli+1

0 0

EPROM- Erasable PROM

DrainSource

Gate

Functional model of ROM

Memory array

Address registerColumn address

decoderL

ine

add

ress

dec

oder

Transitionamplifiers

Transitionlogic

Data register

Data output

Datainput

Refresh Logic

Address

Chip Select

Simplified model

Address decoder

Memory array

Transition logic

Address

Data

Behavioral test

Address generator(Counter)

FunctioningROM

TestifiedROM

Comparisonscheme Functioning/

Non-functioning

Presupposes the existance of a functioning (golden) object (ROM).

Parity check

All words must have even/odd number on 1-s.

0110 00001 11110 1

Paritybits

Detecting faults: 1. Cell stuck – depends on data (If there is a fault

at cell 0 and 0 is being programmed to the slot, it does not detect. Detects usually odd number in s-a-1/0 faults in words..

2. Data line stuck –depends on data. 3. Address decoder fault – does not detect

Functional Testing

It is not necessary to know how memory has been programmed(content of the memory).

Check sum.

Memory ends with the sum of all memory wordsThe number of memory words necessary for preserving the sumdepends on the memory capacityPreserving part of the sum (newer/older) some information is lost.

Detecting faults: 1. Cell stuck – depends on data (If there is a fault at cell 0 and 0 is

being programmed to the slot, it does not detect). Does not detect anything if all words in the memory are 0-s. Bits that have changed in different directions (faulty) mask in different words.

2. Data line stuck – depends on data (if some data line is s-a-0/1 and in all words the value of the respective bit is also 0/1, does not detect; otherwise detects).

3. Address decoder fault –detects if the values of all words are not similar or are not similar at least the wrongly chosen words are not similar.

It is necessary to know a only where the check sum ispreserved. It is not necessary to know the content ofthe memory.