265kb static RAM

[choijimmy]

Hi All,

  I have a question about 256kb static RAM using by PC Engine, Sega mega CD, Sega PAC-S10,etc...

I was told the 256kb *Psuedo* static RAM ( eg, HM6*5*256 )  and  *CMOS* static RAM ( eg, HM6*2*256, HSRM20256) are NOT compatible  ( couple RAM re-sellers told me that )

Because of this, I always replace them with exact same type.

However, yesterday, I have replaced  a Psuedo ram ( Sega Pac-S1) - HM65256  with  CMOS ram HM62256 by mistake.

Interesting enough, I found it works !   

Then I starting thinking indeed they are compatible. ( which is same as what console5 said )

In order to prove this, I try to replace a good  PC Engine 256kb CMOS ram ( HSRM20256LM12 )
with Psuedo ram ( eg, HM65256 ) just for testing. However, this time, it failed. ( eg, scrambled  picture )

Here is the test result:

Sega CD/Pac-S1:   Psuedo ---replaced by ---->  CMOS   ( good )
PC Engine         :   CMOS   ---replaced by ----> Psuedo   ( bad )

Seems 256kb CMOS vs Psuedo static RAM are Not 100% compatible and depends on circuit design/machines.

Am I correct ?

[choijimmy]

Further proof by SNES/SFC  ( using MS62256 CMOS )

Sega CD/Pac-S1:   Psuedo ---replaced by ---->  CMOS   ( good )
PC Engine         :   CMOS   ---replaced by ----> Psuedo   ( bad )
SNES/SFC         :   CMOS   ---replaced by ----> Psuedo ( bad )

So far, the conclusion ( yet ) is  Psuedo can be replaced the CMOS SRAM but Not the other way around.