And again a new Gigatron fan

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Posts: 7
Joined: 17 Dec 2019, 08:03

Re: And again a new Gigatron fan

Post by brian »

Hi Hans,

I have been looking at your Gigatron PCB views in your post dated 28 Feb , one is blue and the other is yellow.

Looking at the expansion patchwork you appear to have wired pins 13 and14 of the 74HCT273 differently.

On the blue version the red wire from pin 14 appears to go to J2 pin 4 and the blue wire from pin 13 goes to J2 pin 3.

However on the yellow PCB this appears to be reversed. Here the blue wire clearly goes to J2 pin 3.

Which is correct, the blue PCB view or the yellow PCB view?

After reading the various posts concerning this topic by others I believe the yellow version is correct but now seek some clarification as to which version is actually correct.

I now live in France but my native language is actually English with some French but not much German.

Your kind response would be appreciated

Posts: 47
Joined: 29 Dec 2020, 16:15
Location: Saxonia

Re: And again a new Gigatron fan

Post by Hans61 »

Hi Brian,
thank you very much for pointing it out. I hadn't noticed it yet. After the design change here:
I wired the blue wrong. Thereby A6 and A7 are swapped, the signals B0 and B1 are responsible for the RAM above the 32kByte memory.
In practice both should work, because the Gigatron doesn't care which physical RAM is mapped into the upper 32k, as long as it is always the same.
But it was not intentional but my mistake. But I will correct it on principle. At the moment I still have problems with the startup of the SD card at the SPI of the Gigatron.
I haven't had time to investigate the problem yet. When I have solved the problem I will definitely make a corrected PCB, if there is none yet. That should be the better solution.
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