US Doubler RAM Modifications

[DavidMil]

Ok.  I've seem two different pictures of the 6810 RAM modifications for the US Doubler Chip.  Which is correct (pictures below)?

One pic shows pin eleven raised on the lower chip and the other doesn't.

 

 

DavidMil

[+Nezgar]

You can do it this "optimized" way:

 

Or even better, use the PCB in this thread that doesn't involve irreversibly modifying the 6810 chips at all:

 

[BillC]

9 hours ago, DavidMil said:

One pic shows pin eleven raised on the lower chip and the other doesn't.

Pin 11 of the 6810P is an active low chip select, /CS1, it won't work unless this pin is pulled low/grounded.

[blacka013]

Go for the boards Nezgar has had manufactured. They are a really professional way of doing the mod.

 

Regards

[DavidMil]

17 hours ago, BillC said:

Pin 11 of the 6810P is an active low chip select, /CS1, it won't work unless this pin is pulled low/grounded.

I thought that pin 11 is an I/O pin (Three to be exact)?  Is there a difference in 6810 chips?

 

DavidMil

[BillC]

13 minutes ago, DavidMil said:

I thought that pin 11 is an I/O pin (Three to be exact)?  Is there a difference in 6810 chips?

 

DavidMil

Pins 2 to 9 are DATA, attached is a datasheet for the MCM6810, pinout is shown on the last page.

MCM6810 datasheet.pdf

[DavidMil]

23 hours ago, BillC said:

Pin 11 of the 6810P is an active low chip select, /CS1, it won't work unless this pin is pulled low/grounded.

I guess my old data sheet info is wrong.  But the IC actually has six chip selects. some low, some high.  If CS1 is not connected,

it just can't be addressed as chip one.  It still has 5 other chip selects it can be addressed as.  I guess this was to facilitate large

numbers of 6810 RAM chips.

 

DavidMil

[BillC]

31 minutes ago, DavidMil said:

I guess my old data sheet info is wrong.  But the IC actually has six chip selects. some low, some high.  If CS1 is not connected,

it just can't be addressed as chip one.  It still has 5 other chip selects it can be addressed as.  I guess this was to facilitate large

numbers of 6810 RAM chips.

 

DavidMil

AFAIK all 6 chip selects must be connected to the appropriate signal level for the chip to be active, leaving any chip select disconnected/floating should disable the chip.

[+Nezgar]

I recall @Kyle22 pointing out that the instructions on the RealDos site are incorrect. At least, it's not how I've ever wired mine. It looks like the one in the OP's 3rd picture.

http://www.realdos.net/US Doubler.html 

[DavidMil]

On 8/13/2021 at 2:01 AM, Nezgar said:

I recall @Kyle22 pointing out that the instructions on the RealDos site are incorrect. At least, it's not how I've ever wired mine. It looks like the one in the OP's 3rd picture.

http://www.realdos.net/US Doubler.html 

This is how my modifications are done (with CS3 trimmed).  If it didn't work, maybe that is why I still have it in my Atari IC's box.

 

DavidMil