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Qbus specs compatibility

RetroNewbie

RetroNewbie

Experienced Member
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Dec 13, 2023
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I am just getting into electronics and I don't fully get voltage levels, max current drain and others parameters used to define devices such as TTL etc.

My question is: can you interface something like an rpi pico directly to the qbus lines?
And if you need something like a line buffer, do you need dec-made parts or just stock parts that are available?

Thank you in advance
 
A pi is (if my memory serves me correctly) is 3.3 Volt tolerant.

Connecting it directly to QBUS (5 Volts) will destroy the pi. You need appropriate buffers between the pi and QBUS.

In terms of the 'type' of ICs used, they have to be capable of supplying and sinking the requisite current, and not be too fast or too slow at switching.

You can use off-the-shelf TTL parts instead of DEC parts. However, the DEC parts were designed/selected for specific characteristics.

Today, beggers can't be choosers. So, if you can't find the correct DEC parts, you have to use what is available...

There are plenty of designs around to help kickstart your project. Look at what they use. But, be aware of the limitations of what you are planning to use (a PI of some desciption).

You may be able to make something that works under certain circumstances, but will it work (or does it need to work) under all circumstances - e.g. DMA?

There is a whole book here...

Dave
 
Last edited:
daver2 said:
A pi is (if my memory serves me correctly) is 3.3 Volt tolerant.

Connecting it directly to QBUS (5 Volts) will destroy the pi. You need appropriate buffers between the pi and QBUS.

In terms of the 'type' of ICs used, they have to be capable of supplying and sinking the requisite current, and not be too fast or too slow at switching.

There is a whole book here...

Dave
Click to expand...
Oh right, that's my bad I forgot about that. So the appropriate level shifters may be enough to interface the pi to the qbus if they can handle the right current?
 
daver2 said:
A pi is (if my memory serves me correctly) is 3.3 Volt tolerant.

Connecting it directly to QBUS (5 Volts) will destroy the pi. You need appropriate buffers between the pi and QBUS.

In terms of the 'type' of ICs used, they have to be capable of supplying and sinking the requisite current, and not be too fast or too slow at switching.

You can use off-the-shelf TTL parts instead of DEC parts. However, the DEC parts were designed/selected for specific characteristics.

Today, beggers can't be choosers. So, if you can't find the correct DEC parts, you have to use what is available...

There are plenty of designs around to help kickstart your project. Look at what they use. But, be aware of the limitations of what you are planning to use (a PI of some desciption).

You may be able to make something that works under certain circumstances, but will it work (or does it need to work) under all circumstances - e.g. DMA?

There is a whole book here...

Dave
Click to expand...
Thank you, I have much reading (and learning) to do.

The idea is to make a really cut down version of a qbone that doesn't set you back hundreds of dollars and can emulate one card at a time (an hard disk emulator for example) So having access to DMA would be important for some functions.
 
I just finished making a Qbus-compatible device using a pi pico - it's a simple sound card for the Soviet clone of PDP 11 named UKNC-0511 and the MPI 16-bit bus, which is a clone of the QBus , I assume. Pi pico emulates a pair of AY-3-8910 PSG chips plus covox (8 bit DAC). The sound is output using two PWM (left and right ch) and a regular RC filter:

photo_2024-02-23_17-59-54.jpg

I am using two 74LVC245 buffers for level-shifting /AD0../AD15 (bi-direction), one 74LVC245 for level-shifting commands (/SYNC,/DBIN,/DBOUT,/BYTE) signals and one 74ALVC05 for driving open-collector /RPLY signal.
If I'm not mistaken, then I have three (!!!) free GPIOs left on the standard pi pico board. This is something to consider if you want to do DMA.

Some video:
(debugging process)
(running demo)
 
Tronix said:
I just finished making a Qbus-compatible device using a pi pico - it's a simple sound card for the Soviet clone of PDP 11 named UKNC-0511 and the MPI 16-bit bus, which is a clone of the QBus , I assume. Pi pico emulates a pair of AY-3-8910 PSG chips plus covox (8 bit DAC). The sound is output using two PWM (left and right ch) and a regular RC filter:

View attachment 1274240

I am using two 74LVC245 buffers for level-shifting /AD0../AD15 (bi-direction), one 74LVC245 for level-shifting commands (/SYNC,/DBIN,/DBOUT,/BYTE) signals and one 74ALVC05 for driving open-collector /RPLY signal.
If I'm not mistaken, then I have three (!!!) free GPIOs left on the standard pi pico board. This is something to consider if you want to do DMA.

Some video:
(debugging process)
(running demo)
Click to expand...
That's amazing! Are there schematics available?
 
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