Atom 2k18 ?

discussion of games, software, hardware & emulators relating to the Acorn Atom
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roland
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Atom 2k18 ?

Post by roland » Tue Jun 05, 2018 11:08 am

Since I still receive request for an updated Atom 2k15 board I'm starting to think about an updated design. With the current we have some issue, regarding to components:
  • The XC95xxXL in PLCC44 package are not available any more
  • The used Godil is also discontinued
  • There's a small mistake in the serial interface
  • I want a joystick connection to the keyboard
About CPLD's
Many other manufacturers also stopped the production of devices in this housing. So we'll have to increase the difficulty of soldering and start using surface mounted CPLD's.

About the Godil
The new devices lack the pins to the 40p socket. They seem hard to find. So I was thinking if it's possible to use the GODIL50_XC3S500E DIL FPGA module (2 x 50 pin IDC) as a replacement. On the Atom board there will be the 2 x 50 pin male connectors so you can simply plug in the new Godil.

Maybe then we also have some additional I/O for hardware handshaking in the serial device. And if there's more room in this FPGA I could also try to add a simple real time clock with the possibility to generate an interrupt every second, minute or hour.

For the Godil part I need advice and support from Hoglet.

Design fault in the serial interface
If you want to use the 3.3V serial input, it conflicts with Rx (pin 12 of the MAX232) which is also an output. So the MAX232 should be removed for 3.3V serial operations. IMHO two diodes can fix this issue.

Joystick connector
There's not a lot of space for an extra connector at the back of the Atom. So I want to replace the 7p DIN socket with a 15p D-type connector which provides joystick, serial and tape I/O.

Other ideas
I will also investigate if the other components are still widely available and components that are (almost) discontinued will also be replaced.

Maybe Robert can also share some ideas about a keyboard. He has constructed a keyboard for his new computer so maybe he can share his experience with us. Hoglet has already a new pcb with the keyboard layout, populated with Beeb key switches.

Please share your thoughts here, but be realistic: there is not much room on the board for many additions like tube ports, user ports etc.
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Elminster
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Re: Atom 2k18 ?

Post by Elminster » Tue Jun 05, 2018 11:42 am

Yes I request implicitly or explicitly at least every few months as I want an Atom but not paying a small fortune for one.

:-)

As a GODIL replacement could you alternatively use the same board that replaced the GODIL on the ICE-T Atombusmon ?

Did my first SMD CPLD at the weekend with help. Not as hard as people tink if you have someone to help you learn.

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Re: Atom 2k18 ?

Post by hoglet » Tue Jun 05, 2018 11:47 am

Are you thinking then that this would be incremental changes to the current design?

I was wondering if it would be worth going for a 3.3V only design.

You could then dispense with level shifers and use a £20-£30 Spartan 6 FPGA module to:
- replace the GODIL
- replace the CPLDs
- replace the 244/245s

There are lots of these available, e.g.
https://www.ebay.co.uk/itm/Mojo-n-V3-FP ... rduino-DIY
https://www.ebay.co.uk/itm/Xilinx-FPGA- ... 1640406811

(The second of these is the board the Duncan referred to in the post above, that we are now using with ICE-T65)

You would end up with the following main chips:
- W65C02 Processor
- W65C22 VIA
- 82C55A PIA (or put this in the fpga)
- 3.3v SRAM
- 3.3v FLASH
- FPGA module
- 3x 74LVC4245 to drive the expansion bus (if you want this to be 5V)
- 18LF4525 PIC for the AtoMMC
- LM358 for tape interface
- MAX232 for serial interface
- LM386 for sound
- 7445 for the keyboard (or do this in the fpga)

Internally, you would then have space to add a Pi connector.

It would also be possible to put the 65C02 and 65C22 in the FPGA, but then when does it stop being an Atom? I'm growing to quite like hybrid systems.

Dave

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Elminster
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Re: Atom 2k18 ?

Post by Elminster » Tue Jun 05, 2018 11:54 am

I think it would be nice to stick with 65C02 and 65C22 as thy are still available new. (Also with CMorley's secret sauce they can be made to go very fast, so I dont think an FGPA gives any particular speed advanage either.)

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Re: Atom 2k18 ?

Post by marcusjambler » Tue Jun 05, 2018 1:52 pm

Fantastic... A new Atom to build =D>

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Re: Atom 2k18 ?

Post by Prime » Tue Jun 05, 2018 2:08 pm

Also the 44 pin VQFP XC95xxXL CPLDs are not that difficult to solder, and would have the advantage that the existing CPLD code could be re-used.

Cheers.

Phill.

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Re: Atom 2k18 ?

Post by roland » Tue Jun 05, 2018 2:22 pm

hoglet wrote:
Tue Jun 05, 2018 11:47 am
Are you thinking then that this would be incremental changes to the current design?
I was wondering if it would be worth going for a 3.3V only design.
I prefer an incremental change to the current design, however I'm not unwilling to use the XC6SLX9 Core Board if we can use that. It's only about half the price of a Godil. It cannot be programmed in-circuit (because of the connector positions) but I don't think that's a big issue.

I don't want a 80% FPGA Atom because there are already lots of those type projects. Another reason is that it's too complex for most people. I guess that some people (like myself) are able to mess around in a CPLD but a FPGA is just a bit too difficult.
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Re: Atom 2k18 ?

Post by gob33 » Sat Jun 09, 2018 3:07 pm

Have a look at the Ultimate 64 replacement board for the C64 by Gideon Zweijtzer.
The 6510 is emulated in an Altera FPGA and keep many ports (HDMI, joysticks, cassette).
Ultimate64.jpg
But on the other side, there is also a replacement board C64 Reloaded MK2 with modern equivalent components which achieve better compatibility than a FPGA.

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Re: Atom 2k18 ?

Post by gob33 » Sat Jun 09, 2018 10:19 pm

In fact, you can do the same with a MISTICA FPGA, a PC keyboard and an Atom core taken/adapted from the Mist.

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Re: Atom 2k18 ?

Post by bprosman » Sun Jun 10, 2018 1:07 pm

Also the 44 pin VQFP XC95xxXL CPLDs are not that difficult to solder, and would have the advantage that the existing CPLD code could be re-used.
Maybe it shows my age but personally also would not go the FPGA route.
Would even consider bringing back the good old 6847. (but then you lack the color option).
For the XC95xx CPLD's you could consider little breakout PCB that fit in a socket.

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Re: Atom 2k18 ?

Post by roland » Sun Jun 10, 2018 7:24 pm

There are some adapters available, however IMHO they are quite expensive and you still have to solder them. The advantage of such an adapter is that you can easily swap the CPLD's:

http://www.epboard.com/eproducts/parts/EPL-0044.htm

The FPGA does much more than only the video, it has also SID audio, mouse interface, (dual) screen memory and serial interface. So replacing it by a good old 6847 removes a lot of features.
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Re: Atom 2k18 ?

Post by roland » Sun Jun 10, 2018 7:31 pm

hoglet wrote:
Tue Jun 05, 2018 11:47 am
There are lots of these available, e.g.
https://www.ebay.co.uk/itm/Xilinx-FPGA- ... 1640406811
(This is the board the Duncan referred to in the post above, that we are now using with ICE-T65)
Can the video and audio signals that are now routed with a separate cable from the top of the Godil also be routed via the header pins?

Is the conversion from Godil to this board a lot of work for you? I expect most of the work is changing the ucf files for the pin layout or do I underestimate the change from Godil to XC6SLX9 board?
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Re: Atom 2k18 ?

Post by hoglet » Mon Jun 11, 2018 5:31 am

roland wrote:
Sun Jun 10, 2018 7:31 pm
Can the video and audio signals that are now routed with a separate cable from the top of the Godil also be routed via the header pins?
Yes the can.

The only reason for using those pins on the GODIL is it avoids passing the VGA video signal through level shifters, which greatly affected the quality.
roland wrote:
Sun Jun 10, 2018 7:31 pm
Is the conversion from Godil to this board a lot of work for you? I expect most of the work is changing the ucf files for the pin layout or do I underestimate the change from Godil to XC6SLX9 board?
It shouldn't be much work at all. Just create a new project file and change the .ucf file. The VHDL design should remain unchanged, unless there is a desire for new features (as there will be plenty of space free).

If you do use one of the eBay boards you will need to replace the 74LS244/245 with level shifers, e.g. 74LVC4245's. You will also need to be careful with signals coming from the 8255 (e.g. FS). Placing 330R (or larger) resistors in line with them should be OK.

Have you decided which board to use?

Dave

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Re: Atom 2k18 ?

Post by roland » Mon Jun 11, 2018 7:10 am

hoglet wrote:
Mon Jun 11, 2018 5:31 am
Have you decided which board to use?
Not yet, the XC6SLX9-board is cheaper and can route the audio and video signals over the PCB which makes it a bit easier. I also have to look at the physical space that both devices need and how they fit on the PCB.
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Re: Atom 2k18 ?

Post by roland » Tue Jun 12, 2018 9:27 pm

Today I have played a bit with KiCad to make an adapter for the CPLD's but whatever I try, it's always too big. I really dislike the surface mounted devices because it's difficult to solder them and also difficult for me to program them for other people who will build an Atom but do not have access to a CPLD programmer. Another disadvantage of the surface mounted parts is that they are hard to exchange when you blow it up. And Atom users always blow up some parts :lol: I even know somebody who destroyed his Godil.... so it's really preferable to have an easy-to-swap device.

On Ebay and Aliexpress there are many sellers who still sell the CPLD's that I need. Does any one have any experience with those devices? Are they really genuine Xilinx CPLD's? I once ordered some GALs and those were quite good.
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Re: Atom 2k18 ?

Post by sirmorris » Wed Jun 13, 2018 8:09 am

I buy most of my xilinx cplds from china via aliexpress. Some have looked odd, with slightly too-large lettering or some other visual artifact that aroused suspicion. They have all been fine though. They all programmed first time, retained their programming, and there have been no weird occurrences or tiny explosions.

I've received used devices before, though. That's what you get when you pay $0.50/unit ;) They were obviously desoldered and already programmed and so needed erasing before I could put them in circuit for programming by PIC. I didn't have a tqfp socket back then so once I worked out what was going on I soldered them to a donor board that had JTAG connections, programmed them in place then desoldered them again and put them into their final place. I only killed one out of the 10 I did, and that was the first one before I'd perfected my technique :lol:

So all-in-all I would happily recommend buying from a seller on Ali.

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Re: Atom 2k18 ?

Post by roland » Wed Jun 13, 2018 12:09 pm

Thanks for your feedback. I'm seriously considering this option. After all, the Atom is not a really life-saving or life-supporting device. Although I'd probably die without it :lol:
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Re: Atom 2k18 ?

Post by Prime » Wed Jun 13, 2018 12:25 pm

If you are going to source parts like this, it may well be worth letting your 'customers' know that they are recycled parts, just incase
there are any problems with them. Personally I'll only supply new parts but that's just me.

As for surface mount parts dying the only examples I've seen personally where with the Mk5 colour board's CPLD being killed by transient signals from the video cable, not really had a problem with any of the Atom RAMROM or DragonMMC boards that could not be attributed to misuse by the user :) Though I do take the point about socketed parts being easier to swap out in that case.

Cheers.

Phill.

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Re: Atom 2k18 ?

Post by roland » Wed Jun 13, 2018 12:48 pm

Prime wrote:
Wed Jun 13, 2018 12:25 pm
If you are going to source parts like this, it may well be worth letting your 'customers' know that they are recycled parts, just incase
there are any problems with them.
I will test them before shipping, as I program them in an already build Atom. So I'm sure that they are working when they leave my house.
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Re: Atom 2k18 ?

Post by bprosman » Fri Jun 15, 2018 1:07 pm

but whatever I try, it's always too big.
Did you try rotating the chip 45 degrees ?


Especially for Roland : special plice :-)

https://nl.aliexpress.com/item/XC9572XL ... autifyAB=0

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Re: Atom 2k18 ?

Post by roland » Mon Jul 23, 2018 8:55 pm

I had a short conversation with the seller of the Spartan boards and we can order those boards with either no headers soldered on in, or have them soldered on the bottom side of the pcb. That would make it possible to do in-circuit programming because the JTAG header should be at the top for inside programming. However, if we mount the board with the components downwards it has lower height so it might fit better in the Atom case.

It can be powered via the USB connector during programming.

This sketch indicates a possible position on the board, the green rectangle. I only have to move the MAX232 and its related capacitors:
IMG_3070.jpg
I assume that the board can also be powered via the 40p headers. ( @Hoglet: ) Is that correct?
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Re: Atom 2k18 ?

Post by bprosman » Mon Jul 23, 2018 9:07 pm

What Spartan board are you referring to Roland ?

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Re: Atom 2k18 ?

Post by hoglet » Mon Jul 23, 2018 9:09 pm

roland wrote:
Mon Jul 23, 2018 8:55 pm
I assume that the board can also be powered via the 40p headers. ( @Hoglet: ) Is that correct?
It can, but see this post for some gotchas:
viewtopic.php?p=176740#p176740

Basically, if you connect the USB port and the Atom power is off, you end up trying to power the whole Atom via USB. That may well damage your laptop.

One option would be to remove the diode D2.

Another option would be to power the board with a flying lead via D1 (and leave Vin on the 40p headers unconnected)

Dave
Last edited by hoglet on Mon Jul 23, 2018 9:09 pm, edited 1 time in total.

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Re: Atom 2k18 ?

Post by roland » Mon Jul 23, 2018 9:26 pm

bprosman wrote:
Mon Jul 23, 2018 9:07 pm
What Spartan board are you referring to Roland ?
I'm referring to this one: https://www.ebay.co.uk/itm/Xilinx-FPGA- ... 1640406811
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Re: Atom 2k18 ?

Post by roland » Mon Jul 23, 2018 9:38 pm

hoglet wrote:
Mon Jul 23, 2018 9:09 pm
It can, but see this post for some gotchas:

Basically, if you connect the USB port and the Atom power is off, you end up trying to power the whole Atom via USB. That may well damage your laptop.
At the moment I,don't see any reason why one would connect a laptop to that board. Especially when the jtag connector is facing the Atom's board. Removing D2 would make the board unprogramble when it is not in the Atom and it must be removed to reach the jtag conector. But I can see the potential problem...
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Re: Atom 2k18 ?

Post by hoglet » Mon Jul 23, 2018 9:42 pm

roland wrote:
Mon Jul 23, 2018 9:38 pm
At the moment I,don't see any reason why one would connect a laptop to that board. Especially when the jtag connector is facing the Atom's board. Removing D2 would make the board unprogramble when it is not in the Atom and it must be removed to reach the jtag conector. But I can see the potential problem...
One possible reason is the board has a USB Uart on it, which might make a nice solution for PC <==> Atom communications.

It's the USB connector that causes the problem, not the JTAG connnector.
Last edited by hoglet on Mon Jul 23, 2018 9:43 pm, edited 1 time in total.

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Re: Atom 2k18 ?

Post by Elminster » Mon Jul 23, 2018 9:49 pm

hoglet wrote:
Mon Jul 23, 2018 9:42 pm

One possible reason is the board has a USB Uart on it, which might make a nice solution for PC <==> Atom communications.

It's the USB connector that causes the problem, not the JTAG connnector.
Could you build some sort of upurs solution around the usb? I am guessing you might be able to drive it faster than the 115k on the user port of beebs.

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Re: Atom 2k18 ?

Post by hoglet » Mon Jul 23, 2018 10:14 pm

Elminster wrote:
Mon Jul 23, 2018 9:49 pm
Could you build some sort of upurs solution around the usb? I am guessing you might be able to drive it faster than the 115k on the user port of beebs.
We can already upload and download at 115K (with CRC).

It doesn't need to use UPURS-style bit-banging, as the GODIL in the New Atom has a proper serial port that runs this fast.

It might even go faster, but then the CRC (and the fact the Atom can be 1MHz) become the bottleneck

The software support for that is in the FPGAUtils ROM:

Code: Select all

FPGAHELP - Shows the version and commands in the ROM.
BAUD <Baud Rate>, Sets the UART Baud Rate (default is 115,200).
UPLOAD <Start>,<End> - Uploads from Atom memory to the UART.
DNLOAD <Start> - Downloads from the UART to Atom memory.
CRC <Start>,<End> - Calculates an Atom CRC over Atom memory.
BEEB - Switches to BBC Mode.
FLASH <Start>,<Bank> - Programs a 4K bank of the FLASH from Atom Memory.
I do miss my Atom.... been doing far to much Pi stuff recently :(

Dave

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Re: Atom 2k18 ?

Post by roland » Tue Jul 24, 2018 12:16 pm

hoglet wrote:
Mon Jul 23, 2018 9:42 pm
It's the USB connector that causes the problem, not the JTAG connnector.
I know that :lol: But if we do not use the USB for communication then the USB is only used for programming the device and then the board will be out of the Atom.
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Re: Atom 2k18 ?

Post by hoglet » Tue Jul 24, 2018 1:07 pm

roland wrote:
Tue Jul 24, 2018 12:16 pm
I know that :lol: But if we do not use the USB for communication then the USB is only used for programming the device and then the board will be out of the Atom.
I don't think you can program the device over USB.

Actually, a nice fix might be to drive the two Vin pins on the header via a schottky diode. Then no reverse powering would be possible. Vin is just used to drive the 3.3V regulators, so feeding in 4.5V should be fine. There are already schottky diodes (MBR0530 = 0.5A) on the other power feeds.

Dave
Last edited by hoglet on Tue Jul 24, 2018 1:14 pm, edited 4 times in total.

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