Thread: Ortonview PCB
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Old 28th Jun 2021, 5:34 pm   #10
Slothie
Octode
 
Join Date: Apr 2018
Location: Newbury, Berkshire, UK.
Posts: 1,287
Default Re: Ortonview PCB

Quote:
Originally Posted by Mark1960 View Post
I think you have the address lines to the RAM from the wrong side of the buffers. This would prevent access to the RAM from the SCMP.

Is the diode supply switching to the RAM something you have already tested? I have experimented with putting the switching in the ground connection using a bc108 to avoid voltage drop as this also disables write enable when main supply is off. I wasn’t convinced this was really working well. I think I prefer to use a MAX818 or similar to also disable chip enable, though it might not be simple to connect the reset output to the SCMP via the edge connector.

If you have space use a small slide switch for the write protect instead of just a two pin header.

I don’t think you want pin 18 and 21 on the ram connected.
The annotations on the buses are correct, so the memory will connect to the unbuffered address bus, but your right in that the diagram is misleading. I will have to redraw the blue line connecting the memory to rest of the circuit to make this clearer. perhaps changing the labels from UAx to BAx would be more appropriate too.

I have tried using diodes to route power to chips but not this one specificaly. However the M5M5117 operates down to 4.5v so the ~0.2v schottky diode drop should not cause problems. If it does, I'll just remove the battery function and jumper the diodes.

Nice spot on pin 18/21, not sure how that happened.

Thanks for spotting these things, its exactly why I post this!
Ian
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