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visrealm / pico-56

The HBC-56 (65C02/TMS9918A/AY-3-8910 retro computer) fully emulated on a Raspberry Pi Pico
https://youtube.com/@TroySchrapel
MIT License
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Q1 (2N4401) question #3

Closed g8kuw-tv closed 6 months ago

g8kuw-tv commented 6 months ago

Hi Troy - I have built a PICO-56, and it's almost working...

Is Q1 in the Pico-56 schematic shown the wrong way around? I can't see how KBD ground will be pulled low when 3v3 is present.

Thanks

Steve

visrealm commented 6 months ago

Hi Steve. I think you're right.

However, I just checked a couple of my built examples and confirmed my 2N4401s are indeed oriented as shown in the schematic and it does appear to work fine.

I will update the schematic.

Thanks Troy

g8kuw-tv commented 6 months ago

Thanks Troy!

(I wasn't sure if this was an appropriate place to ask questions.)

vslinuxdotnet commented 5 months ago

Hello, Sorry about this question but, what is the propose of this transistor to enable GND in keyboard? The 3v3_en is to enable (default) the PWD of 3.3v, witch is always high, so the transistor is always on. Regards, VS

visrealm commented 5 months ago

The power and reset buttons are connected to 3.3v_en so the transistor effectively powers off the keyboard when the PICO-56 is "off" (or reset).