WHy pattern A and Pattern5 Tetscases are used to test memory ?Any special reason ?

WHy pattern A and Pattern5 Tetscases are used to test memory ?Any special reason ?

Yes, look at the binary equivalents:

5 = 0101
A = 1010

They are alternate ones and zeroes so writing and reading them gives the quickest check for stuck bits. Normally 0x55 and 0xAA are used to make up 8 bits.

Brian.

Just to check the stuck-at fault, the pattern doesn't matter. All 0 followed by all 1 and checkerboard pattern have the same efficiency.
It's most probably because it creates crosstalk situation on the bit lines, however, if bit[2n] and bit[2n+1] aren't next each other like all the even bits are on one side of the memory, and odd bits are on the other side of the memory, checkerboard doesn't cause much crosstalk. So, it depends on the memory layout.

Hai thanks for the reply ...
I need some more clarification like ,,,,,, If suppose memory is stuck at 1(say)...How this pattern(0xAA) finds the bug and how other pattern say 0x11(say or any other pattern) wont find that bug.

If a bit in a memory location is stuck at 1 and you write a number to it which has that bit set you are not achieving anything. Reading it back as '1' would show it as being correct regardless of whether the bit was stored or not. If you write a '0' to a location where the bit is stuck at '1' and read it back you see '1' which obviously tells you the zero wasn't stored properly.

Taking an extreme example, suppose you wrote '0' to a non-existent memory chip and then read it back and found '0', would that tell you the memory was OK ?

Lostinxlation is quite right, nor only does writing 01010101 then 10101010 quickly show a stuck bit, it also shows some addressing errors and shorts between adjacent cells.

Brian.

Hi Brain ,
1)If suppose a bit in one of memory location was stucked at 1 .
Pattern 0x1 and then 0x0 will also find the bug.Instead of 0xA then 0x5 ...we can use 0x1 then 0x0 for all scenerios of stck at 1 and 0.Is it correct?

2) One more doubt.
In order to test 8k memory .how many Read and write operations are required.
How we can calculate no of Read and write operation required to test a specific memory.
Can u please tell. to test 8k memory(say)
What r the testcase scenarios we require,How many read and write opeartions required.

I think you may be confusing bits and bytes. Normally when testing memory, a whole byte (8-bits) or sometimes multiples of bytes are tested in one operation.
When you refer to pattern 0x1 what exactly do you mean? In normal 'talk' a pattern 0x1 would refer to a byte which in binary is 00000001, in other words 8 bits with just the least significant bit set.
To test a memory by writing a single bit and reading it back to confirm it would be failing to test the remaining 7 bits.

For example, I suppose the bit I highlight below is faulty:

0010000

if you write 1 to the LSB and read it back it will be OK, the same if you write 0 to it, the memory address is however, faulty because bit 4 is stuck.

Using 0x55 and 0xAA is writing to all 8 bits, 01010101 then 10101010 so all the bits are checked for being stuck in one write, read and compare operation.

There are many kinds of memory faults, that is why you see tests using 0x33 and 0xCC and random numbers being used. Sometimes the fault is not a bit stuck but an address line stuck so for example you could think you were writing to 8k of memory but due to the fault you were actually writing to the same 1k eight times. There are also timing faults and refresh faults which all require specific checks to find them.
At its simplest, a data only check of an 8k memory would be 8192 writes followed by 8192 reads of one pattern then 8192 writes and reads of a complimentary pattern, 16384 writes and 16384 reads in total.

Brian.