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62256 Ram Problem - not able to read the contents

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shashavali_m

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62256 ram

Hi
I have interface the 32K RAM 62256 to a controller 89C55, but i am not able to read the contents from it. Dont know whether its written properly or not. Its always read lower byte of the address which it needs to access.

Plz help me how to sort out this problem.
Please share if you have any RAM test program

Thanks in Advance.
 

hock

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62256latch

for testing the RAM
for start of memory to end of memory
{
write 0xAA (1010101010)
NOP
read from memory location
check if != 0xAA --> memery bad


write 0x55 (0101010101)
NOP
read from memory location
check if != 0x55 --> memery bad

if no error memory is OK
}

hock
 

IanP

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port 62256

Maybe the problem lays in the hardware.
I hope you are aware that Port[0] is the multiplexed low order Address and Data bus during access to external memory and you have to use 74373 demultiplexer to latch the low order address (A0 to A7) ..
See attached picture ..
Rgds,
IanP
 

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