Feature Addition Wishlist

[Cube Central]

Howdy!

I thought I would create a thread listing some of the things I would like to see on future revisions of the ZiNC80 SBC1.  This way other folks could add to it.

1)   An on-board barrel jack replacing the screw terminals.  The screw terminals aren't my favorite and would enjoy a different connection.

2)   Along with the barrel jack, an option to install a pair of capacitors and an LM7805 or PSU5A switch-mode voltage regulator similar to the RC2014 Backplane Pro

3)   With these, an on-board SPDT ON/OFF switch.

4)   A way to change the clock speed.  I was wishing there was a way to run at a slower speed when running stability tests.

5)   An connector and jumpers to use an external clock, again for testing.

6)   An option when purchasing the SBC1 to include a ZIF socket for the 27C512 ROM (at location U9) as part of the kit.  There is room for it now, just enough!

That's all I have been able to think of so far.  Cheers!

    -Randal   (at CubeCentral)

[Jon Langseth]

On Friday, May 25, 2018 at 6:55:10 PM UTC+2, Cube Central wrote:

Howdy!

I thought I would create a thread listing some of the things I would like to see on future revisions of the ZiNC80 SBC1.  This way other folks could add to it.

1)   An on-board barrel jack replacing the screw terminals.  The screw terminals aren't my favorite and would enjoy a different connection.

There's two reasons why I went with the screw terminals. First, having screw terminals allow for flexibility in mounting, encapsulating and teeing off power for other parts of the system. Second, I hate barrel connectors ;) If a barrel connector is something many request, I can consider a revision where optional holes and board-space is provided, but that will require moving some of the other components in that corner of the PCB around.

 

2)   Along with the barrel jack, an option to install a pair of capacitors and an LM7805 or PSU5A switch-mode voltage regulator similar to the RC2014 Backplane Pro

My logic for not adding holes/provisions for one is combined with the screw terminal. If you need to tee off power to a different part, like a CF-adapter, you will want to get the same 5V power out to that part. This means using an off-board 5V power will be needed, and will also be able to provide cleaner VCC with a higher current capacity than what a 7805-style device (Typically limited to 1A even on most switch-mode replacements. And a switch-mode 7805 replacement that close to the CPU is asking for noise-related problems).

Again, if this is a much desired feature, it is possible to include, but I do not see the advantage unless there's a barrel-connector on the board.

 

3)   With these, an on-board SPDT ON/OFF switch.

This does not make much sense to me without a barrel connector and a voltage regulator. And if those are added, there's not much space for a switch unless I really change the layout. On one of my builds, I have a cord-mounted power switch on the 5V line (of the type you can find on lamps etc), and on another I have an enclosure where the power switch is mounted.

 

4)   A way to change the clock speed.  I was wishing there was a way to run at a slower speed when running stability tests.

There are two ways to change the clock speed. Changing the oscillator, or removing it and injecting your own clock via either the oscillator socket or the expansion bus.

5)   An connector and jumpers to use an external clock, again for testing.

External clock can be fed in through the oscillator socket, the expansion bus (or, come to think of it, via any of the SIO Clock jumpers pin 3. For example, default jumper settings set SIOA to be clocked by CTC, leaving pin 3 of J2 as an available Clock pin. As your external clock ground also needs a connection point, you can tee it in on the screw terminal, or use pins 7 or 8 on either of the PIO Parallel ports.

6)   An option when purchasing the SBC1 to include a ZIF socket for the 27C512 ROM (at location U9) as part of the kit.  There is room for it now, just enough!

Once I have a reliable source for a reasonable ZIF socket for the upcoming ROM cartridge kits, I will make your suggestion an option on the kit!

 

I hope you don't find my responses too unreasonable. Good suggestions all round. To be honest, most of the points 1-5 were things I considered when laying out RevD (the current revision), but decided not to include to avoid feature creep/featuritis, and keep it in line with my general idea.

[Angus Bliss]

Jon, I wonder why you did not use the FTDI cables 5v connection instead of having a NC.
I agree re the barrel connector. Too easy to think its an Arduino and plug something more than 5 volts in.
I would suggest a USB connector. No voltage or polarity issues then.
I do agree that there should be header so as to power those CF cards that don't have pin 20 connected.
If you used FTDI you would need a jumper to disconnect it if using the other connector.
Fortunately the power draw of the Linc80 is small - be a lot less if the CF Card had dimmer LEDs.

[Jon Langseth]

There are two reasons I did not connect the "VCC" line of the "FTDI cable" connector. 

Firstly, because the USB1.x spec default current draw is limited to 100mA, and my prototype w/o CF card or expansions was pulling 150mA. The shipped kits draw less than this, but someone building from bare PCB could end up in the same range of current, and I wanted to be absolutely sure that my design wasn't killing other people's USB controllers/ports/FTDI-dongles. This is a concern that is not solved by a disconnect-jumper. It's less of an issue considering most systems have USB2 ports these days, but I'd rather be safe to be honest.

The second reason is to avoid back-powering and/or clashes between linear power regulators if the main power is used at the same time as the "FTDI-connection" power is hooked up. This is of course resolved by a jumper, but still an issue that one time you forget to remove the jumper, and fry either your directly attached  power supply or your USB port.

A final and third reasoning is minor: 5V tolerant 3v3 USB TTL-Serial dongles. This is simply to reduce the potential confusion.

[angus...@gmail.com]

Jon,

If you were to do a Mk II of the Linc80, what would be the possibility of adding a Zilog DMA controller. Then we would have a complete set of the Zilog family of chips. Moving more that 24 bytes is more efficient with DMA.

I know the board would need to be enlarged to do that but that should not be an issue? Maybe easier to fit Randals ZIF socket.

It would be good to know some of the thinking behind the design. For example, the SIO/2 - is this because of availability because it supports all the old synchronis protocols, therefore creating a market. A DART would seem to have been more appropriate.

I thought I saw some mention of a graphics card. I used to have a TDL graphics card - two pages of 25 by 80 plus graphics, Just a huge number of TTL logic chips on two S100 cards. It was I/O mapped and I don't think it suffered for that. Or with things like Raspberry Pi zeros, is that the best way to go. I know they do simple terminal emulation to a HDMI output but no knowledge of how to do graphics. Be scary if one had to dirty ones hands with LINUX. 

You of course could also use a USB connector for power, as per my previous post. If its good enough for the Raspberry Pi, it should suit the Linc80. 

Seems if you build it uses will appear. The Stephen Cousins use of the PIO for a LCD screen says something. Just about to try that out myself.

Regards,

Angus

[Jon Langseth]

It's been a while since your post, apologies for not getting back on the subject earlier.

I'll touch on your second point first. Quite a bit of the reasoning/thinking behind the design is probably readable on my private blog posts about my journey. The series should be all collected under the URL http://defcon.no/tag/homebrew/?order=asc 

Basically, the concept was to make a version of G. Searle's fairly basic design, with inspiration from the RC2014 project, but in Single-board format, with IM2 at it's core and with the Z50Bus as it's expansion bus. Apart from going with IM2 on an SBC, I wanted to deviate as little from the basic RC2014/G.Searle concept as possible on the LiNC80 SBC1, and originally planned to use the standard Searle ROMs. This would allow the LiNC80 to have quite a lot of existing, compatible software available already. During the project, Steve Cousins came on-board with his brilliant SCM. This change from simple BASIC ROM to a fully featured and expandable monitor happened after I had spun up the first pre-production boards, so the hardware was reasonably set at that point.

I haven't quite decided yet, but as the name "LiNC80 SBC1" may indicate, I may design an "SBC2" at a later point. The Zilog DMAC will definitely be a part of an SBC2, and I am contemplating a
RomWBW-compatible paging mechanism to replace the paging (implemented but not really used) present on the SBC1. An SBC2 will probably still use the SIO/2, mostly for parts availability. Additionally, the SIO provides the same asynchronous serial functionality as a pure "UART" like the DART, but additionally provides HDLC/SDLC and CRC in one package. If a DART or UART is needed, I provide prototyping cards for Z50Bus :)

In regard to graphics, I really hope that someone tries their hand at a Z50Bus based display adapter. The "Membank" connector and associated paging-mechanism was included to facilitate memory expansion, and possibly a memory-mapped framebuffer. Possible directions may be either framebuffer based or I/O mapped. Implementation can be discrete, as you mention, or maybe something around the V99x8 VPDs or a Parallax Propeller. Even a Z50Bus-implementation of Geoff's VT100 "terminal" could be interesting. I've been experimenting a bit on some ideas myself, but haven't really gotten any real progress. If I were to come up with something "official", it would have to be based on current, in-production and in-stock parts.

I'm noting the wishes commented in this thread for inclusion on a possible SBC2, should I get to it. The power connector stands out as a "must change", and is a relatively "cheap" item on the list, so an SBC2 would include provisions for SPDT-switched barrel jack with LDO regulator, screw terminal and a small (probably micro) USB connector. I'm tempted to design in provision for a CH340 chip as well, even if it is a SOP/TSOP device. Regarding board space, I actually think I should be able to make a LiNC80 SBC2 not be much different in form factor, as I haven't really made the current board as small as possible :) It'll have to be a bit larger to fit an additional 40-pin IC for the Z84C10 DMAC, but not much.