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ashtons
PostPosted: Thu May 20, 2021 7:21 am 
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Greetings!

After a conversation almost a month ago, I decided to start moving away from CBM and over to an SD card and SCSI for my computer's storage interfaces. SD should be easy - just need to adapt this SPI interface and I should be good to go. SCSI, however, may pose a problem.

While the same person also created a SCSI interface, I'm not entirely sure that it would fit or work in my computer project, as it is a portable system and therefore the circuits need to be as compact as possible. So, any SCSI interface hardware would need to be compacted so it could fit. I'm not entirely sure if the CS/A65 SCSI interface can be compacted enough to fit into a portable computer.

Should I just dump SCSI and go SD-only, or is there a way to fit a SCSI interface?

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BigDumbDinosaur
PostPosted: Thu May 20, 2021 7:58 am 
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ashtons wrote:
Greetings!

After a conversation almost a month ago, I decided to start moving away from CBM and over to an SD card and SCSI for my computer's storage interfaces. SD should be easy - just need to adapt this SPI interface and I should be good to go. SCSI, however, may pose a problem.

While the same person also created a SCSI interface, I'm not entirely sure that it would fit or work in my computer project, as it is a portable system and therefore the circuits need to be as compact as possible. So, any SCSI interface hardware would need to be compacted so it could fit. I'm not entirely sure if the CS/A65 SCSI interface can be compacted enough to fit into a portable computer.

Should I just dump SCSI and go SD-only, or is there a way to fit a SCSI interface?

Might be a tad easier to answer your question if we knew what this project was all about.

BTW, my POC units have SCSI. Unlike André's approach, which was to bit-bang the SCSI bus (definitely not trivial), I used a 53CF94 SCSI controller to build my host adapter. It was a two chip solution, plus a clock.

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ashtons
PostPosted: Thu May 20, 2021 12:30 pm 
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BigDumbDinosaur wrote:
ashtons wrote:
Greetings!

After a conversation almost a month ago, I decided to start moving away from CBM and over to an SD card and SCSI for my computer's storage interfaces. SD should be easy - just need to adapt this SPI interface and I should be good to go. SCSI, however, may pose a problem.

While the same person also created a SCSI interface, I'm not entirely sure that it would fit or work in my computer project, as it is a portable system and therefore the circuits need to be as compact as possible. So, any SCSI interface hardware would need to be compacted so it could fit. I'm not entirely sure if the CS/A65 SCSI interface can be compacted enough to fit into a portable computer.

Should I just dump SCSI and go SD-only, or is there a way to fit a SCSI interface?

Might be a tad easier to answer your question if we knew what this project was all about.

BTW, my POC units have SCSI. Unlike André's approach, which was to bit-bang the SCSI bus (definitely not trivial), I used a 53CF94 SCSI controller to build my host adapter. It was a two chip solution, plus a clock.


Fair point.

  • Planning to run the W65C02 at 8, 4, or 2 MHz (8 MHz preferred)
  • 32K SRAM
  • 4 ROM areas: 4k banked service ROM area (new, had to shrink MMIO from 8k to 4k), 8k banked external ROM area, 8k banked program ROM area, 8k system ROM area
  • 4k MMIO area: 2x W65C22, W65C51 (you told me to switch manufacturer to Rockwell, or go with a different RS232 chip, on a different thread), NHD-240128WG-ATFH-VZ# graphical LCD, an atmega as a keyboard controller (to keep things simple), interrupt logic, a DAC-08 which will be hooked into a speaker once I figure out what speaker to use
  • Power Supply: 9V battery or center-positive DC jack

At the end, the computer should be relatively small and portable (at least as small and as portable as a TRS-80 Model 100).

(I may edit this in the future - don't know how much information is exactly necessary.)

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BigEd
PostPosted: Thu May 20, 2021 1:00 pm 
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If you want SCSI, is that because you have a particular device in mind to attach to it? If it's just storage, I would think SD card should be enough.
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floobydust
PostPosted: Thu May 20, 2021 1:24 pm 
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If you only need data storage, I would also suggest looking IDE (Compact Flash), as it's even easier to interface to the 6502 than SD. CF Cards can be powered from 3.3V or 5V without any changes as well.

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BigDumbDinosaur
PostPosted: Thu May 20, 2021 6:09 pm 
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ashtons wrote:
  • Power Supply: 9V battery or center-positive DC jack

At the end, the computer should be relatively small and portable (at least as small and as portable as a TRS-80 Model 100).

If this is to be a battery-powered unit I would not use SCSI. The SCSI bus operates at relatively high current levels when in use, especially if passive termination is used. A CF card interfaced via IDE will be much more economical with power and should have sufficient performance. Save SCSI for a machine powered from the line.

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ashtons
PostPosted: Thu May 20, 2021 11:39 pm 
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A bunch of useful advice. I'll look into implementing an IDE interface for CF cards, since I want there to be some options for storage.

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floobydust
PostPosted: Thu May 20, 2021 11:57 pm 
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ashtons wrote:
A bunch of useful advice. I'll look into implementing an IDE interface for CF cards, since I want there to be some options for storage.


If you don’t want to re-invent the wheel, you can just use mine, which is both here on the forum and my GitHub page.

viewtopic.php?f=4&t=6223&start=15#p82125

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BigDumbDinosaur
PostPosted: Fri May 21, 2021 6:45 am 
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floobydust wrote:
ashtons wrote:
A bunch of useful advice. I'll look into implementing an IDE interface for CF cards, since I want there to be some options for storage.

If you don’t want to re-invent the wheel, you can just use mine, which is both here on the forum and my GitHub page.

viewtopic.php?f=4&t=6223&start=15#p82125

This is an offer you shouldn't refuse. There comes a point in every project where knowing when to make use of prior art makes the difference between wishing it was working and actually seeing it working. flooby's implementation looks pretty good to me and is not difficult to implement. As he suggested, don't reinvent the wheel.

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ashtons
PostPosted: Fri May 21, 2021 9:45 pm 
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BigDumbDinosaur wrote:
floobydust wrote:
ashtons wrote:
A bunch of useful advice. I'll look into implementing an IDE interface for CF cards, since I want there to be some options for storage.

If you don’t want to re-invent the wheel, you can just use mine, which is both here on the forum and my GitHub page.

viewtopic.php?f=4&t=6223&start=15#p82125

This is an offer you shouldn't refuse. There comes a point in every project where knowing when to make use of prior art makes the difference between wishing it was working and actually seeing it working. flooby's implementation looks pretty good to me and is not difficult to implement. As he suggested, don't reinvent the wheel.


I learned the "don't reinvent the wheel" lesson the hard way on a completely unrelated software project. I'm going to use flooby's implementation.

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fachat
PostPosted: Sun May 23, 2021 12:17 pm 
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BigDumbDinosaur wrote:
ashtons wrote:
Greetings!

While the same person also created a SCSI interface, I'm not entirely sure that it would fit or work in my computer project, as it is a portable system and therefore the circuits need to be as compact as possible. So, any SCSI interface hardware would need to be compacted so it could fit. I'm not entirely sure if the CS/A65 SCSI interface can be compacted enough to fit into a portable computer.

Should I just dump SCSI and go SD-only, or is there a way to fit a SCSI interface?

Might be a tad easier to answer your question if we knew what this project was all about.

BTW, my POC units have SCSI. Unlike André's approach, which was to bit-bang the SCSI bus (definitely not trivial), I used a 53CF94 SCSI controller to build my host adapter. It was a two chip solution, plus a clock.


Just nitpicking.... it's byte-banging ;-)

But seriously, for modern design I would not include SCSI anymore. Also, not sure if any of the modern devices is even compatible with the SCSI async mode I used.

In fact I wouldn't think an IDE solution would be necessary. Use a small SPI interface in a CPLD or use the VIA shift register to connect an SD card and you should have all the storage u need with a simple design and low power requirements.

André

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BigDumbDinosaur
PostPosted: Mon May 24, 2021 6:25 am 
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fachat wrote:
BigDumbDinosaur wrote:
ashtons wrote:
Greetings!

While the same person also created a SCSI interface, I'm not entirely sure that it would fit or work in my computer project, as it is a portable system and therefore the circuits need to be as compact as possible. So, any SCSI interface hardware would need to be compacted so it could fit. I'm not entirely sure if the CS/A65 SCSI interface can be compacted enough to fit into a portable computer.

Should I just dump SCSI and go SD-only, or is there a way to fit a SCSI interface?

Might be a tad easier to answer your question if we knew what this project was all about.

BTW, my POC units have SCSI. Unlike André's approach, which was to bit-bang the SCSI bus (definitely not trivial), I used a 53CF94 SCSI controller to build my host adapter. It was a two chip solution, plus a clock.

Just nitpicking.... it's byte-banging ;-)

Shift to the left, shift to the right, do the heebie-jeebie, it's byte, byte, byte. :D

Quote:
Also, not sure if any of the modern devices is even compatible with the SCSI async mode I used.

Async mode is still part of the parallel SCSI standard. I run my drives in async mode, and they are all U160 and U320 units attached to the 50-pin cable with a 68-to-50 adapter.

The 53CF94 supports the 10 MHz sync mode specified in X3-131-1994 (SCSI 2), which I didn't implement in the firmware because the SCSI bus in sync mode can outrun the 65C816 operating at 20 MHz. A DMA controller is needed to take advantage of sync mode.

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ashtons
PostPosted: Tue May 25, 2021 8:16 pm 
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BigDumbDinosaur wrote:
Shift to the left, shift to the right, do the heebie-jeebie, it's byte, byte, byte. :D


The 6502 version of the Cupid Shuffle?? Or do I have the wrong song/dance?

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