When is the 10K RAM resistor needed?

[msknight]

I don't quite understand the need for the 10K ohm resistor that is being put between pins 27 and 28 of larger RAM chips on the zeddy. Do i really need to use it?

Grateful for any enlightenment please.

[1024MAK]

Are you using battery back up?

If no, then the 10kΩ resistor between pins 27 and 28 is not needed.

Pin 27 will always be driven by the Z80 /WR control line.

This is not true however if the RAM is being powered by a backup battery, in which case, the battery supply (pin 28) would need to pull-up pin 27 to try to prevent garbage being written to the RAM during the time that the rest of the board is powered down.

Mark

[msknight]

Ah! That explains it. The resistor is present on the myretrostore 16k upgrade, so I wonder why they put it in. They also have an extra capacitor in there as well. I'm not sure why.

[1024MAK]

People are following the details that are widely available on the internet, even though those details are slightly misleading.

Mark

[msknight]

People are following the details that are widely available on the internet, even though those details are slightly misleading.

Mark

That's one reason why I'm asking the silly, awkward questions... in the hope of getting my own details slightly less misleading than everyone elses