Author Topic: Double-even reads from HM628128ALP EEPROMs  (Read 814 times)

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Offline Aggressive_DoughnutTopic starter

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Double-even reads from HM628128ALP EEPROMs
« on: March 23, 2019, 03:14:21 pm »
I arbitrarily grabbed a tube of HM628128ALP EEPROMs from the shelf, slapped one in my little arduino-based programmer, and gave it a quick test and... oddly... I get no odd values read from the ROM in my little displayContents table, instead I get the data from address 0 showing for both address 0 and address 1, the data from address 2 for both 2 and 3, and so on:

000:  2a 2a 0d 0d 2f 2f 34 34  39 39 1a 1a 14 14 0c 0c
...

When I read the odd values outside of a loop, they all read fine.  After a while of fooling around I split the ROM-reading loop into an even loop and an odd loop and everything works great.

Has anyone ever seen this before?  I don't see it as a "feature" in the datasheet anywhere.  I get this for all of my HM628128ALPs but not other EEPROMS.
 

Offline Deni

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Re: Double-even reads from HM628128ALP EEPROMs
« Reply #1 on: March 23, 2019, 03:42:25 pm »
HM628128ALP is SRAM, not EEPROM isn't it? Although that should not affect reading...
 

Offline newbrain

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Re: Double-even reads from HM628128ALP EEPROMs
« Reply #2 on: March 24, 2019, 03:05:09 pm »
Yes, it's a 16kB CMOS static ram (neither ROM nor EEPROM).

As the programmer is self built, and I presume coded: is it complying with the needed setup and hold times (i.e. CSx, OEn or address to data read)?
Is the A0 connection good and low resistance?
Can you check signal integrity with a scope?
Which speed grade are those RAMs?
Nandemo wa shiranai wa yo, shitteru koto dake.
 

Offline amyk

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Re: Double-even reads from HM628128ALP EEPROMs
« Reply #3 on: March 24, 2019, 05:57:09 pm »
Check the configuration of the A0 pin. If it is set to open-drain (maybe with only the internal pullup enabled) then this behaviour is possible.
 


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