New Atom - What now?

[hoglet]

That looks very nice.... I can see I'm going to have to start saving my pennies for this, and for one of your Pi Econet server setups!

[KenLowe]

Almost there. Just waiting for the last few pieces...

Various Atom Boards - Part Built

[KenLowe]

Finished laying out the Combined Econet / AtoMMC module. A couple of points of note:

• I've replaced the diodes on the SDCard module with a 74LS125 level shifter. I've basically copied the Arduino SD card reader circuit.
• To make routing a bit easier, the pull up on the Station ID is powered from the 3V3 rail, and not the 5v rail. I don't think it really makes any difference which rail I use.
• I intend to carry out the functions of the AToMMC 74AC139N in the CPLD. Is there anything specific I need to be aware of given the original selection of the AC series IC?
• I've not written the CPLD code yet, so I'm hoping all the logic will fit as I've manually assigned all the pins to simplify routing.
• Learning from previous projects, I've wire Phi2 into one of the global clocks; GCK3 (Pin 1).

As always, thought / comments are most welcome...

Schematic

Layout

Layout with flood fill

Top View

3D View

3D View with Econet Module plugged in

Econet_AtoMMC.pdf

High resolution Schematic

(107.79 KiB) Downloaded 7 times

[IanS]

As always, thought / comments are most welcome...

Can't fit an AEH52 as they only have short pins, it won't fit over the 5-pin DIN socket

http://chrisacorns.computinghistory.org ... grade.html

[roland]

I didn't check each signal but in general your design looks good. What worries me is that you are using component that are hard to get at the moment, like the microcontroller, the CPLD and voltage regulator. Or do you have a secret source?

[KenLowe]

Can't fit an AEH52 as they only have short pins, it won't fit over the 5-pin DIN socket

http://chrisacorns.computinghistory.org ... grade.html

Yeah, I did think about providing a header for a remote DIN socket, which would allow use of a short pin Econet module, but I'm a bit short of space. I'll have a look again to see if there's anything I can do. If you're using one of my Econet modules, I can supply it with short pins and a DIN socket. Best of both worlds :

viewtopic.php?f=8&t=24307

What worries me is that you are using component that are hard to get at the moment, like the microcontroller, the CPLD and voltage regulator. Or do you have a secret source?

No secret source! Intention was to re-use the PIC that comes with the AtoMMC. The CPLDs would come from AliExpress and the other SMD components would be supplied with the board from JLCPCB. JLC have plenty of these parts in stock.

[KenLowe]

Can't fit an AEH52 as they only have short pins, it won't fit over the 5-pin DIN socket

http://chrisacorns.computinghistory.org ... grade.html

With a bit of creative adjustment to the Combined DIN5 / Ethernet socket footprint, it looks like I should be able to add a third PCB header option into the footprint. So, in that location you should be able to either install a DIN5 socket, Ethernet socket (wired to 'Blundell' standard for Econet) or a 5 pin 90 degree header. This is what it would look like. Does that adequately address your comment?

Updated footprint for Econet connector

Updated 3D image showing 5 pin 90 degree header

[KenLowe]

Hi folks,

I have a couple of questions about the original AtoMMC circuit that I've copied over to the combo Econet / AtoMMC board.

Q1 - Crystal
I've based my AtoMMC circuit on this schematic:

https://site.acornatom.nl/download/mmc4/atommc3-th.pdf

which is similar to this circuit:

https://site.acornatom.nl/atom_handleid ... schema.pdf

This second schematic includes a crystal & caps that are tied into the OSC1 & OSC2 pins on the PIC. The crystal & caps are not present on the first schematic, and I have not implemented this on my board. Are these actually required for anything?

Q2 - Tx & Rx pins
The first circuit diagram shows the Tx & Rx pins wired out from the PIC. I've included a 3 pin header on my board that is tied to the PIC Tx, Rx and Gnd pins. I assume this would be used for debug purposes?

Q3 - 10 pin header
What is the purpose of the 10 pin header that is connected to pins 33 thru 40 (and Vcc / Gnd) on the PIC? I initially assumed this was a programming header, but I then saw an AtoMMC v4 image that suggests it's a 'Joystick or General I/O' header. Has anything been developed in the PIC / Atom that uses this I/O?

[hoglet]

Q1 - Crystal
This second schematic includes a crystal & caps that are tied into the OSC1 & OSC2 pins on the PIC. The crystal & caps are not present on the first schematic, and I have not implemented this on my board. Are these actually required for anything?

The PIC used in AtoMMC has a couple of clocking options:
- an external 10MHz Crystal (allowing the PIC to run at 40MHz)
- in internal oscillator that runs the PIC at approximately 32MHz

Both options work.

When programming the boot loader firmware into the PIC, there is a clock configuration register than needs to be programmed accordingly (as far as I remember).

Q2 - Tx & Rx pins
The first circuit diagram shows the Tx & Rx pins wired out from the PIC. I've included a 3 pin header on my board that is tied to the PIC Tx, Rx and Gnd pins. I assume this would be used for debug purposes?

Yes, it can be used for logging output.

Q3 - 10 pin header
What is the purpose of the 10 pin header that is connected to pins 33 thru 40 (and Vcc / Gnd) on the PIC? I initially assumed this was a programming header, but I then saw an AtoMMC v4 image that suggests it's a 'Joystick or General I/O' header. Has anything been developed in the PIC / Atom that uses this I/O?

It's a general purpose 8 bit I/O port; there are commands in AtoMMC to make use of it:
- *PBD sets the direction
- *PBV reads or writes the current value

It's typically used for a Joystick - several games in the Archive have been converted to work with AtoMMC connected joysticks.

Which PIC part are you planning to use?

The AtoMMC2 uses a PIC18F4525 - this is what most of us have, and was was included in Roland's Atom2K15 project.

The schemtic you are are basing this on uses a different PIC: a PIC16F874P.

Does boards with the latter option actually exist in the wild?

Dave

[hoglet]

(note my edit about which PIC you are using....)

[hoglet]

I think it's a mistake that those schematics show a PIC16F874.

That part only has 192 bytes of RAM.

AtoMMC2 uses a PIC18F4525 with 3968 bytes of RAM, pretty much all of which are used!

Dave

[roland]

AFAIK all the diagrams mention a PIC16F874P but all AtoMMC boards are equipped with the 18F4525. Even this diagram from 2010 mentions the 874...

It would be nice to have an alternative type as Microchip will need a few months to ship new PICs for our AtoMMC and I recently bought the whole Mouser stock (all three of them)

[hoglet]

It would be nice to have an alternative type as Microchip will need a few months to ship new PICs for our AtoMMC and I recently bought the whole Mouser stock (all three of them)

What about the PIC18F4610?

Digikey is showing 99 in stock.

Dave

[roland]

Mouser has 68 in stock so that would be enough for the time being. Would this one require a different firmware version? I expect it does..

[hoglet]

Mouser has 68 in stock so that would be enough for the time being. Would this one require a different firmware version? I expect it does..

Hmmm, unfortunately it doesn't seem to have any internal EEPROM.

This would mean *CFG and *PBD values would have to be hard-coded (which is probably no great loss).

Dave

[KenLowe]

I know China isn't the first choice for everyone, but if you want to take a bit of a gamble, what about this:

https://www.aliexpress.com/item/32902085054.html

[KenLowe]

Q1 - Crystal
This second schematic includes a crystal & caps that are tied into the OSC1 & OSC2 pins on the PIC. The crystal & caps are not present on the first schematic, and I have not implemented this on my board. Are these actually required for anything?

The PIC used in AtoMMC has a couple of clocking options:
- an external 10MHz Crystal (allowing the PIC to run at 40MHz)
- in internal oscillator that runs the PIC at approximately 32MHz

Both options work.

When programming the boot loader firmware into the PIC, there is a clock configuration register than needs to be programmed accordingly (as far as I remember).

Q2 - Tx & Rx pins
The first circuit diagram shows the Tx & Rx pins wired out from the PIC. I've included a 3 pin header on my board that is tied to the PIC Tx, Rx and Gnd pins. I assume this would be used for debug purposes?

Yes, it can be used for logging output.

Q3 - 10 pin header
What is the purpose of the 10 pin header that is connected to pins 33 thru 40 (and Vcc / Gnd) on the PIC? I initially assumed this was a programming header, but I then saw an AtoMMC v4 image that suggests it's a 'Joystick or General I/O' header. Has anything been developed in the PIC / Atom that uses this I/O?

It's a general purpose 8 bit I/O port; there are commands in AtoMMC to make use of it:
- *PBD sets the direction
- *PBV reads or writes the current value

It's typically used for a Joystick - several games in the Archive have been converted to work with AtoMMC connected joysticks.

Which PIC part are you planning to use?

The AtoMMC2 uses a PIC18F4525 - this is what most of us have, and was was included in Roland's Atom2K15 project.

The schematic you are are basing this on uses a different PIC: a PIC16F874P.

Does boards with the latter option actually exist in the wild?

Dave

Thanks for all the responses.

• I think I'll try to squeeze an external crystal / caps onto my board, just in case it's ever needed.
• I've updated my schematic to reflect the PIC18F4525 instead of the PIC16F874P that was on the original AtoMMC schematics.
• I will be using the PIC18F4525 on my new board. The intention is to remove the PIC from my existing AtoMMC board.

[hoglet]

Another possibility: PIC18F46Q84-E/P
- 40 Pin DIP Package that looks compatible
- runs at upto 64MHz
- 5V power
- 64KB Program memory (FLASH)
- 8KB Data memory (RAM)
- 1KB EEPROM

Mouser has 217 in stock at £2.74 each:
https://www.mouser.co.uk/ProductDetail/ ... IvFw%3D%3D

The only issue might be programmer support.

Dave

[roland]

I know China isn't the first choice for everyone, but if you want to take a bit of a gamble, what about this:

I recently gambled for 10 working HM62256-12 static RAM chips. I received them and my tester shows two defective. That's 20%: So I am not gambling with parts that costs about €9.50 (including shipping). However, if I order only one then it's impossible to receive 20% faulty pics

[KenLowe]

I'm hoping not to get into a big debate about this, as I've seen differing opinions about it on this board (eg here and here). General consensus before I get the soldering iron on it, have I got the internal connector (PL7) the right way round???

PL6 / PL7

[roland]

Officially this is the wrong way around. Pin 1 of the connector is +5V and is closest to the border of the PCB; pin 32 is 0V and is next to the printer connector.

[KenLowe]

Ok. Thank you. I've now turned it around 180 degrees, and done the same with the Atom Tube board.