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Old 17th May 2021, 10:51 am   #23
RhinoDevel
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Join Date: May 2021
Location: Schleswig, Schleswig-Holstein, Germany
Posts: 3
Default Re: Raspberry Pi as a storage device for a PET.

Hi there,

it is great to read about my little project, here!

I'd like to add the following to the discussion:

Quote:
It doesn't appear that they've specified any transistor types, but it should work with an small signal ones like BC547 (NPN) & BC557 (PNP) etc.
Yes! BC547 & BC557 are recommended in the README (https://github.com/RhinoDevel/cbmtap....7.0/README.md).

Quote:
I'd also be inclined to build it a bit more permanently on a bit of matrix board / veroboard, as parts are all quite low-cost, rather than using prototyping breadboard.
That is always a good idea (mentioned in the README, too)!
The breadboard is used to avoid "unnecessary" soldering to not scare away beginners (at least that was the intention).

Quote:
And you could always use a read-made level converter board, for both directions ...
One of the project goals was to use discrete components for the interface, only (to keep it as simple as possible).

Quote:
The only thing I could wish for is, if you were going to connect something as complex and powerful as a Pi, it might as well be emulating the FDD (ie, functionally equivalent to the SD2PET) rather than the datasette as that would seem like a better way to use one.

The Pi would then have to be interfaced to the IEEE 488 port, and that would present its own complications. It might be worth looking around to see if someone has already done it.
CBM Tape Pi is no real tape or disk emulator.
But it uses the tape port, only (you should be able to connect real disk drives at the same time for copying, etc.).
It also has the wedge and its fast mode (~2.5 Kbyte/s).
And it is compatible with VIC 20 and C64, too.

***

About the design of the Pi to CBM READ pin:

The VIC 20 (6522/CA1) and PETs (6520/CA1) do not seem to have a pull-up
resistor (neither internal nor external), but the C64 (6526/Flag) definitely has
one.

R4, R5 and T1 make the connection work with and without pull-up resistor.

By the way, the Pi to CBM SENSE line is always connected to a pull-up,
otherwise a button press would not be detected (C64: 6510/P4, VIC 20: 6522/PA6,
PETs: 6520/PA4). That is way there is no PNP for SENSE.

Please correct me, if I am wrong here or if there is a simpler way to solve this
problem.
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