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Today, I learned that the #Commodore 1351 mouse used pulse position modulation to send X/Y coordinate data to the #SID chip.

The SID chip (if clocked at 1MHz) samples its POTX, POTY lines every 512us. It does this by discharging each POTx line's capacitor to ground for 256us, then floats the line for another 256us. A corresponding counter increments monotonically until the voltage across the capacitor exceeds 2.5V.

The mouse starts out by floating its POTx outputs high, waiting for the SID to bring POTX (specifically) low. When this happens, the mouse then drives the POT line low and waits for 320us to elapse, making sure to exceed the 256us sync window.

It then waits an additional 0 to 127 microseconds depending on the coordinate it wants to send. The mouse then drives the POT line high for a microsecond or two, slamming the capacitor in the computer to 5V. This also freezes the A/D counter, since it exceeds the 2.5V threshold.

After that procedure, the mouse floats its output again, knowing that the POT line is once again in a state where it can detect the SID chip's synchronization pulse, and the process starts all over again.

This means that, on each POT line, 7 bits of data are transferred every 512us, for an equivalent serial data rate of 13671.875 bits per second. There are two POT lines in operation at the same time, for a total data rate of 27343.75 bps.

Not too shabby!

#C64 #C128

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RT @linsley_barbara
Telephone sheep, using old cords & phones, by Jean Luc Cornec brilliant ๐Ÿ‘๐Ÿป๐Ÿ˜‚๐Ÿ‘‡

The founder of all these upscale places is a celebrity chef who published a dozen cookbooks ๐Ÿ˜ฏ
@nicocesar @srevinsaju

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Turns out it's a ring of restaurants with presence in various cities around the world:

@nicocesar including Boston!
@srevinsaju and Bahrain! ๐Ÿ‡ง๐Ÿ‡ญ

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Bernie boosted

@codewiz @patrick @lubimaer @5tr34k_ @ilwoody it looks like this is a thing people are working on: I'm skeptical as to whether that many users would actually use this though since it'd almost certainly be more involved than the status quo of creating an account on an instance.

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Bernie boosted

already 2 years old, but amazing blog post on reverse-engineering physical geomery of hard disks using micro bench marks:

Bernie boosted

Bow down before me, for I have successfully completed A TASK today, and it's not even 10am. I am powerful and unstoppable!


Actually, my head is spinning, I think I need to go stare vaguely into the distance outside for a bit and then suddenly realise it's lunchtime.

Landed. And passed through US immigration without showing a passport or other ID: just face recognition ๐Ÿ˜จ

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Bernie boosted

Today I'm relocating to and looking for long-term housing.

I have zero friends in LA. Any fedinauts living around here?

Today I'm relocating to .

I have zero friends here and I'm looking for long-term housing. Any fedinauts from LA around here?

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