BBC ports to the Atom

discussion of games, software, hardware & emulators relating to the Acorn Atom
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roland
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BBC ports to the Atom

Postby roland » Sat Nov 26, 2016 9:30 pm

Since we're getting more and more BBC peripherals available for the Atom I was thinking about an extension board for the Atom that provides us the BBC ports, at least at the hardware level. This is a rough sketch of such a board:

Schermafbeelding 2016-11-26 om 18.46.01.png


The CPLD will take care for some address decoding for nPGFC and nPGFD alike signals (e.g. #BExx, #BFXX) and an 8th printer bit (partly in software, you first write the value of the 8th bit to this port and then print the character at the normal way). If leave out the 8th printer bit then a GAL will probably do as well whicht makes the design a bit easier. The buffers at the tube port can be 74LS245 for matchbox co-pro's or 74LVC245 for Pi Zero co-pro.

These are my thoughts about such an interface. What are your thoughts about this? (Please don't answer: "Why don't you get a beeb? :lol: )
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Re: BBC ports to the Atom

Postby 1024MAK » Sat Nov 26, 2016 9:43 pm

roland wrote:What are your thoughts about this? (Please don't answer: "Why don't you get a beeb? :lol: )
Okay, instead, I answer: can you get this and an Atom in a Beeb case? :lol:

If you think this will be useful to yourself, hey, why not?

Would the printer port be the Atom printer port, or the Beeb printer port?

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Re: BBC ports to the Atom

Postby lazarusr » Sat Nov 26, 2016 10:51 pm

Would it not make sense to put a 6522 on the board to drive the printer and user ports? That would maximise the level of hardware compatibility.

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Re: BBC ports to the Atom

Postby Prime » Sun Nov 27, 2016 8:21 am

lazarusr wrote:Would it not make sense to put a 6522 on the board to drive the printer and user ports? That would maximise the level of hardware compatibility.


Well the Atom alreaddy has a 6522 internally, which drives the Atom's printer port, but is also connected to it's external bus (where the proposed board connects), which is I assume how Roland was going to drive it. However as the beeb has 2x 6522s then a second one would be an advantage, as it could be used just for driving the beeb peripherals.

Cheers.

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Re: BBC ports to the Atom

Postby oss003 » Sun Nov 27, 2016 12:06 pm

Hi Roland,

that's a nice idea, maybe a serial, an econet and an analogue port can be added.
And extra hardware: soundchip, speechchip or an FPGA to emulated these peripherals.

Greetings
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Re: BBC ports to the Atom

Postby roland » Sun Nov 27, 2016 12:59 pm

This board will probably quite large if only the connectors are populated on the board. There have to go 16 address lines, 8 dataline, 8 control lines and 20 I/O lines from right to left over the board so IMHO peripherals like a sound and speech chip should be connected to one of the buses. That is why I came up with this idea, to have a 1 MHz bus to connect Robert's BeebOPL board to the Atom.

Concerning the printer port, I prefer the Atom port because if I implement the BBC printerport then the printer-routines in the rom have to be updated.
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Re: BBC ports to the Atom

Postby roland » Mon Feb 27, 2017 12:58 pm

I have made a first version of this board. It contains:

  • An additional 64p connector for Atom extensions
  • An Atom compatible printer port (Atom VIA A-port)
  • A BBC user port (Atom VIA B-port)
  • A 1MHz bus interface
  • A Tube interface
  • A Pi-tube interface

Please have a look to the circuit diagram and the pcb. I have double checked the positions of the connectors but I prefer if another pair of eyes have a decent look if the connectors have the right position.

You can also let me know if you're interested in this board. The costs of the PCB will be about €20,00 (without shipping to your home address) when I order five boards.
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Re: BBC ports to the Atom

Postby roland » Tue Feb 28, 2017 12:37 pm

I notice many downloads of the drawings. Do the viewers have any feedback?
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Re: BBC ports to the Atom

Postby lazarusr » Tue Feb 28, 2017 12:43 pm

You ask that people double check the position of the connectors. But I don't understand why that matters.

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Re: BBC ports to the Atom

Postby roland » Tue Feb 28, 2017 3:27 pm

lazarusr wrote:You ask that people double check the position of the connectors. But I don't understand why that matters.


I think my English grammar is lacking here a bit. It's not the position of the connectors whether they are left or right or so but the position that pin 1 is really pin 1. Maybe, the orientation of the connectors is a better word. In my first versions I had swapped the rows of all connectors so if you mounted a normal connector than pin 1 of the connector would be soldered to pin 2 on the PCB.

I hope this explains my concerns a bit....
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Re: BBC ports to the Atom

Postby lazarusr » Tue Feb 28, 2017 7:57 pm

roland wrote:
lazarusr wrote:You ask that people double check the position of the connectors. But I don't understand why that matters.


I think my English grammar is lacking here a bit. It's not the position of the connectors whether they are left or right or so but the position that pin 1 is really pin 1. Maybe, the orientation of the connectors is a better word. In my first versions I had swapped the rows of all connectors so if you mounted a normal connector than pin 1 of the connector would be soldered to pin 2 on the PCB.

I hope this explains my concerns a bit....

Now I understand exactly. I have spent hours worrying about the same thing. I shall have a look at my Beebs when I get home.

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Re: BBC ports to the Atom

Postby hoglet » Tue Feb 28, 2017 10:11 pm

I'll do some checking of this tomorrow as well.

Dave

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Re: BBC ports to the Atom

Postby lazarusr » Tue Feb 28, 2017 11:48 pm

Looking in from the front of the Beeb, pin 1 is always in the upper right corner of the connector. So look at the PCB from the edge, pin 1 should be in the row furthest back. So, in short, it looks to me like your PCB is correct.

You can, of course, check your schematic against the service manual. But that, broadly, looks correct to me too save that I don't really understand what is going on with pin 21 of the Printer Port (which is not connected on the Beeb).

Hope this helps.

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Re: BBC ports to the Atom

Postby roland » Wed Mar 01, 2017 4:53 pm

I copied the printer port from the Atom to avoid modifying the print routine. Pin 21 is the /busy signal from the printer.
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Re: BBC ports to the Atom

Postby roland » Sun Mar 12, 2017 7:57 pm

I added another port, the board has now also room for the Atom PL8 connector which can be used for the real time clock Big Benny or an Econet adapter. As the Atom2k15 already has an AtoMMC at #B400 this connector will be put in another address block, perhaps #B410 - #B41F or the complete #B5xx block. It's just a matter of programming the GAL.
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Re: BBC ports to the Atom

Postby 1024MAK » Tue Mar 14, 2017 2:01 am

Please add me to the interested in buying one list :D

Mark
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Re: BBC ports to the Atom

Postby roland » Tue Mar 14, 2017 10:21 am

1024MAK wrote:Please add me to the interested in buying one list :D
Mark


I'll do that. Anybody else interested?
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Re: BBC ports to the Atom

Postby oss003 » Tue Mar 14, 2017 10:29 am

Yep, I also want one.

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Re: BBC ports to the Atom

Postby Multiwizard » Tue Mar 14, 2017 5:20 pm

Yes please... :D


Greetings, Wim... :-)

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Re: BBC ports to the Atom

Postby roland » Sun Mar 19, 2017 9:22 pm

Today I had a last check to convince myself that all connectors have the right orientation and that all pins of these connectors are correct. I made a small modification for the 8th printer bit: CB2 was not buffered while I have three ports left in a 74LS241. So I buffered the 8th printer bit via CB2. I also enlarged the board a bit to make the connectors fit better and at last I added a few mounting holes.

Tomorrow I'm going to order five or six boards and I expect to receive them by the end of May ... just in time for our TechSat ... I hope ....

Schermafbeelding 2017-03-19 om 22.15.23.png
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Re: BBC ports to the Atom

Postby roland » Tue Mar 21, 2017 7:56 pm

I have ordered five boards, so I will have one spare. Now waiting for delivery.
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Re: BBC ports to the Atom

Postby Multiwizard » Tue Mar 21, 2017 8:11 pm

roland wrote:I have ordered five boards, so I will have one spare. Now waiting for delivery.

I'm exited already... =D> \:D/


Greetings, Wim... :-)

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Re: BBC ports to the Atom

Postby roland » Sat May 20, 2017 8:02 pm

A few weeks ago I have received my boards from MakePCB. As usual they look perfect. Due to family matters I was very busy in my non-working hours but today I finally finished soldering the board. As usual with boards of this manufacturer the board is very easy to solder. :D

IMG_1984.JPG


As usual I made a design error. The 64p "output" connector is too far away from the border. Either I should have placed it nearer to the edge, or I should have made a slot for it. Anyway, I manually made a slot for it like this picture shows you:

IMG_1969.JPG


The first test was powering the board and check the voltage on the individual ic's. That's all fine. Even the Pi Zero blinks its led. When I poke around on the B-port of the VIA then the user-port-pins change their logical state. Also very fine :)

In the next days I will program the GAL and check if the tube ports both work and if the 1 MHz bus and the PL8 equivalent also has some life in it.
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Re: BBC ports to the Atom

Postby roland » Mon May 29, 2017 9:37 pm

I have been doing some tests today, especially the address decoding and it looks fine. However, the Pi Zero didn't respond to any command, except for BREAK (the led flashes).
It turns out to be a design fault in the pcb, which is caused by an error in the schematic diagram:

pcbug.png


The select pins have different names on the buffer and the Pi connector. So this track is not routed on the board. It's easy to repair, just a piece of wire between pin 11 of the connector and pin 7 of U2. After adding that wire, the PI zero starts printing the Atom's output to the second monitor :)

In the next days I'll try to connect the matchbox copro board and the BeebOPL. For both boards I have to rebuild the software due to other I/O addresses.
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Re: BBC ports to the Atom

Postby hoglet » Mon May 29, 2017 9:41 pm

Looks like good progress there Roland. :D

With the PCB error, did KiCad's schematic DRC not give an error?

Dave

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Re: BBC ports to the Atom

Postby roland » Mon May 29, 2017 10:16 pm

hoglet wrote:With the PCB error, did KiCad's schematic DRC not give an error?


I can't remember whether I ran a DRC or not. You'd expect a warning about unused networks or something like that. I will it run one of these days...
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Re: BBC ports to the Atom

Postby roland » Tue May 30, 2017 8:30 pm

I have run the ERC in KiCad and it gives 46 warnings. Most of them are from pins that are really connected and also for the +3.3V for the 74LVC245 buffers. But those are powered by the Pi Zero but I didn't tell KiCad. So I must have overlooked the unconnected PiTube select line - or I didn't do the check at all .... can't remember :(

But KiCad is not to blame for this mistake ](*,)
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Re: BBC ports to the Atom

Postby roland » Thu Jun 01, 2017 8:37 pm

The BeebOPL board works fine on the new 1 MHz bus port on the Atom \:D/

I notice my PiZero get quite warm, is this normal in our setup as a copro for the Atom or Beeb?
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Re: BBC ports to the Atom

Postby hoglet » Thu Jun 01, 2017 8:43 pm

roland wrote:I notice my PiZero get quite warm, is this normal in our setup as a copro for the Atom or Beeb?

How warm is warm?

If you use the debug kernel, it will report (to the serial port) it's temperature on each reset (of the Pi).

I can check mine tomorrow.

Dave
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Re: BBC ports to the Atom

Postby roland » Thu Jun 01, 2017 9:45 pm

The serial output says the core temperature is 48.96˚C after the PiZero was 10 minutes powered on, waiting for an instruction from the Atom. Then I let it display a memory dump for a few minutes and the temperature went down to 47.96˚C and later up to 50.84˚C.
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