PAL-2 daughter board and expansion board physical design

[GN Liu]

Hi community,

I just finished a model about the PAL-2's expansion board design. Is it okay, or do you have any better ideas? Please share your thoughts!

Thanks! 

Liu

[Nils Andreas]

How about some connectors for real Kim expansions? Like the Pal-1 motherboard from zoggins?

nils

Von meinem iPhone gesendet

Am 21.02.2025 um 08:28 schrieb GN Liu <liuga...@gmail.com>:

Hi community,

I just finished a model about the PAL-2's expansion board design. Is it okay, or do you have any better ideas? Please share your thoughts!

Thanks! 

<Screenshot 2025-02-21 152153.png>

Liu

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<Screenshot 2025-02-21 152153.png>

[Raaalf]

Hello Liu,

there should be mounting rails for the expansion cards on the PAL-2 daughter-board.

Mounting rails

Greetings

Ralf

[GN Liu]

Nils,

There will be an edge connector in the plan.

The KIM-1 is taller than the PAL-2. I originally considered placing the two KIM-1 edge connectors on the left side of the daughterboard, but I feel that the size and shape wouldn’t look very aesthetically pleasing. Instead, the edge connectors will be implemented as a dedicated 90° expansion board, installed on the leftmost socket of the current daughterboard design. Additionally, the PAL-1 expansion connector will also be a 90° expansion board on the daughterboard.

What do you think about this approach?

Liu

[GN Liu]

Hi Raaalf,

In my plan, the sockets on the daughterboard are two 2×20 pin sockets (2.54mm pitch) per row, with a 20mm gap between them. I’ll test some dummy boards on the daughterboard to see if they can be securely fixed.

Mounting rails are a great way to hold the expansion board in place, but since the daughterboard has no case, I’m unsure how effective the mounting rails will be.

For my future plan, the daughterboard will have an installation option as the back panel of a boxed PAL-2 system. By changing the rightmost connector to a pin socket, the PAL-2 can function as a baseboard within the enclosure, with mounting rails built into the box.

Liu

[Neil Andretti]

So you plan to implement the original KIM egde connectors like an adapter that fits into the motherboard.

Sounds good!

I forgot the link in the last post:

https://retro-spy.com/product/pal-1-motherboard-expansion-kit/

[GN Liu]

Yes, according to the old PAL-2 plan post and one of Hans’ suggestions, I believe it’s the same size as the KIM-1 connector. However, Zoggins’ design is more compact. I’m not sure whether the actual size of the KIM-1 is crucial. If not, the board could be made smaller to fit the height of the PAL-2.

[Hans Otten]

A daughter board for the PAL-2 can be done in many ways. The proposal by Liu is a flat on the table solution.
Expansion cards are 'standing' on the daughterboard (and need supports at the sides). 

Alternative could  be the 'cage' solution as done with the original KIM-1. A passive backplane (with power distribution) and expansion cards with the same size as the KIM-1.
Expansion cards are placed underneath the PAL-2 with I/O at the edge. 
See this for examples: 

Hardware expansions – Retro Computing 

Advantage is compact size, and the 'cage'  takes care of a sturdy mechanical support of cards. And it has the 70ties look and feel!

The backplane will have 3 or more PAL-2 Application and Expansion connectors.

But it might be not so easy to construct a cage.

Now what kind of connectors on the daughterboards to use might be also worth a discussion.
The only available boards at the moment are the KIM-1 I/O and KIM-1 ROM/RAM boards by Retrospy. But they are of limited value to the PAL-2 owner. 

 

What we need of a daughterboard  for the PAL-2 are now:

- a good and reliable way to connect the USB serial adapter

- alternative power source connector

- a ROM to map in at higher memory. 

- a switch for TTY/LED and Keyboard switch

-  SD card adapter 

- 1541 IEC connection

- bus connectors for expansion cards 

Optional may be (on expansion cards)

- one or two 6522 VIA's

- serial adapter like 6850 or 6551 

- KIM-1 compatible audio circuitry (if you have the one wire adaption to the PAL-2 I have described)

- whatever you may think of

Another way of expanding, with the help of Eduardo Casino, to connect his MTU bus solutions for the KIM-1, to the PAL-2. Take a look at

GitHub - eduardocasino/kim-1-mtu-ram-rom: KIM-1 RAM/ROM Expansion Board for the MTU Backplane

GitHub - eduardocasino/kim-1-programmable-memory-card: KIM-1 Programmable Memory Board for the MTU Backplane

GitHub - eduardocasino/kim-1-mtu-motherboard: Buffered expansion backplane for the KIM-1 that follows MTU's standard for cards like the K-1008 Visable Memory

His KIM-1 to MTU motherboard just needs a PAL-2 connectors to KIM-1 connectors adaptation. 

[David Carlin]

Liu,

Thank you for the work on the PAL-1 and PAL-2 !

Would you consider a small board for the Application connector with a usb or barrel jack for power, and a port - DB9 or USB - for TTY connection?  That is my main concern,  hooking up the dupont wires incorrectly.  Thanks!

--

[Hans Otten]

I support the request by David for a small simple board for just the application connector, with  USB to serial connector and a TTY switch (and perhaps a small experiment pad)

[Eduardo Casino]

The MTU bus just needs the Expansion connector and two lines from the Application connector: K7 and DECEN.

So, if the PAL-2 expansion board had just a KIM-1 type, edge pcb, expansion connector on the left, it could be possible to attach the simpler MTU unbuffered expansion card (https://github.com/eduardocasino/kim-1-mtu-expansion-card) and take the two lines with DuPont cables from the appl. connector.

However, I have yet to study the PAL-2 schematc to see if Liu's modifications to the RAM/ROM address decoding are fully compatible with what an MTU card expects (I think they are, but I have to double check)

Eduardo.

[GN Liu]

Like this small simple one?

[Hans Otten]

Some suggestions:

 The USB to TTL you deliver with the PAL-2 has 5 male pins, of which 4 are relevant (GND<,VCC, TxD, RxD)

• I would suggest a 5 pin female pin connector to put the USB device in. If you can find a right angled one, so that the USB device can lay flat with the USB-C at the left, it would be perfect and reliable.
• LEDs? Ok, a power led perhaps . The VCC, RxD and TxD have LEDs on the USB device.
• The small adapter blocks access to any of the other pins on the application connector. Solution  I see with other daughter boards is  an 22x2 pin male connector on the daughterboard, with all pins of the application connector available, accessible and documented with text on the PCB.
• The barrel connector and USB power should be switchable to prevent shorting, add another switch there.
• What is on the 6 pin connector at the bottom?

 Hans

[GN Liu]

Hi Hans,

The reason I plan to use a 6-pin connector is that I want to be compatible with more USB-to-TTL converters (even though the one I have comes with a 5-pin converter). I designed this interface based on the FTDI module with the most pins that I know of. I provide a jumper configuration for the four actually needed pins to adapt to different converters. Do you think this is necessary?

The LEDs serve a similar purpose. My idea is that if someone is using a adapter without LEDs, such as an FTDI cable, these three LEDs on the interface board can serve as indicators.

Are you suggesting adding an application interface the same as the one on the PAL-2 board to the daughterboard, for example, placing it on the left side of the daughterboard to use the available pins in other scenarios?

You’re right—adding a power selection switch makes sense.

The 6-pin component without a 3D model is not a connector; it is a switch used to select between local or serial connection.

Liu

[Hans Otten]

This is what I propose, a minimal but practical and safe setup using what is available in your kit

- 5V USB or external with switch

- your USB serial card flat on the PCB with a female right angle 5 pin 

- SD card connector for PA1 - PA4 famle
- switch TTY - Keypad/LED

- all pins on application connector to 2x22pin male

I made a mockup showing how it might look

[Jeremy Starcher]

One of the ideas I was walking on:

Putting a Pi Pico-W (wifi) on my breakout board and letting it serve a similar purpose to to the digital cassette recorder.

Let it take over the TTY/LED switch and the serial port to upload stuff onto the Pal-2 for me.

It would also be accessible over wifi so I could upload from my desktop to the Pico.

[Jeremy Starcher]

Now I"m wondering if I could halt the CPU and use DMA to load, make things a little faster...

Hmmmm

[Hans Otten]

Re DMA: you can halt a 65C02, not a 6502. If you look at the Sorbus Computer or the Neo6502 you can see the Pico control the 65C02 by stopping the 6502, tri-stating the busses  and taking over the data and address bus (via RDY and BE pins).. 
There are more examples of a device like the Pico or Arduino board doing the initial setup and after laoding memory let the 65C02 carry on. 

No such luck with the 6502. 

Of course you can replace the 6502 with a WDC65C02 on the PAL-2. There are no bus drivers that may prevent taking over the 65C02 and blocking access to the busses.

[Jeremy Starcher]

True -- but there are ways to do DMA on the MOS 6502 as well, they are aren't as easy.

Some early video outputs would use the RDY line to pause the CPU for an instruction and then do DMA every other clock cycle.

Time things really carefully and do your DMA based on the PHI/1 clock.

Nowhere near as nice, of course, as the 65C02's lines, but .. well, we live with what we have.

Not sure what the RESET line on the 6502 does, but if that puts the but into HIGH-Z while it runs, then you could just pause the CPU entirely then let it out of RESET.  Since you'd only be doing DMA to load a program, I wouldn't be worried about trashing the register state.

Heck, you could even load the executable address in the system so all the user has to do is press [GO] or enter [G].

To view this discussion visit https://groups.google.com/d/msgid/pal6502/4b7e137f-05c6-4dc7-a33d-aa258d73fd5en%40googlegroups.com.

[Jeremy Starcher]

AH, the link I couldn't find earlier

https://retrocomputing.stackexchange.com/questions/12718/how-to-implement-bus-sharing-dma-on-a-6502-system

[Dimitri]

To allow me to continue using the RIOT gadgets I designed, I have come up with the following:

I haven't assembled my PAL-2 yet (and currently do not have the PAL-2 PCB to hand), but looking at the schematic, it looks like PA6 is not available from the expansion connector.  Is this correct?

Many thanks,

Dimitri

[Dimitri]

Of course, I meant PB6!

D.

[GN Liu]

Thanks, Hans. I’ll rethink it based on your layout.

Dimitri,

PB6 is absent because the 6530 on the KIM-1 used it for chip select, so the KIM-1 doesn’t have PB6 on the application port. This pin on the PAL-2 is a bonus pin (like the expansion card for PAL-1). I think we can add a jumper wire to an unused pin on the PAL-2’s application connector for PB6. (Now, we might have two jumper wires on the PAL-2…)

Liu

[Dimitri]

A jumper wire sounds like a reasonable workaround. Please could you suggest which currently unused pin I should use for this - I don't want to pick one myself and find that you had chosen that exact pin for a different purpose.

Many thanks,

Dimitri

[GN Liu]

Based on my notes, I’ll route PB6 (U3) to R on the Application connector and PB7 (U2) to 19 on the Expansion connector.

Best,

Liu

[Dimitri]

'R' sounds great, thank you! 

 I have updated my design accordingly (and added a power source select switch as per Hans' suggestion):

Gerbers will be made available as soon as I've had a chance to test this irl.

:D

[GN Liu]

my updated version daughter board mini.

Hans, I think the micro SD card adapter is not very suitable for this version and will be on the bigger board. I bought some adapters compatible with 5V input for testing, which are slightly bigger than yours.

Liu

[Dimitri]

This looks great!  Just one observation, would it be more aesthetically pleasing if the TTL/KEYBOARD switch was horizontal and on the edge of the board (like power select), rather than vertical?

D.

[Kande Laber]

Just for the record.
Personnally, I am used to work with  6 pin USB to TTL serial adapters (an example is shown in the attached picture).
6 pin adapters are frequently used e.g. with Arduinos and Z80 kits.

Best regards

[GN Liu]

Hi D.,

My idea is that pushing the stem toward the TTL connector means serial mode, while pushing it in the opposite direction means keyboard mode. Now that you mention it, placing it horizontally also makes sense, switching toward the mainboard could mean keypad mode, and the opposite direction could mean TTL ;) 

I’ll see how it looks in reality.

Liu

[GN Liu]

Hi Kande,

The mini version of this daughterboard is designed as a quick-start board, providing a convenient and stable power supply and serial access for the PAL2. Since the PAL2 comes with a 5-pin TTL converter, the interface definition of this mini board follows the pin definition of that converter.

Looking back at the previous design, I originally planned to use the FTDI interface definition. However, that approach might have been more complex and required additional soldering, so I opted for the current design instead.

Liu

[Kande Laber]

OK, "... Since the PAL2 comes with a 5-pin TTL converter,"
That is a good argument. I ignored that, sorry.

[GN Liu]

The sample board feels good!

[Dimitri]

That looks great ... a definite must have for all PAL-2 owners!

And do give me a shout if you'd like to test some more gadets...

:D

[Hans Otten]

Awesome!

[David Carlin]

Dimitri,

Can you tell me more about these expansion boards?  One seems to have a speed synthesizer chip, the other an IEC connector? (Commodore floppy drive?)

Do they plug into the 16-pin header on the PAL-1 RIOT expansion board?  And perhaps would also plug into the PAL-2 mini daughter board?

Thanks!

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[Dimitri]

David,

They are two of the gadgets I created for the PAL-1 RIOT Expansion Module, and yes, you are right, the first one is a SP0256 based speech processor. The other one is an IEC interface that can be used with Commodore disk drives or, I guess, printers.  They plug in to the PAL-1 RIOT board using a small adapter (compatible with Liu's gadget adapter). It should all work unchanged with the PAL-2 Daughter Board Mini ... I think.

:D

[Dimitri]

... and there are other gadgets too, including a Real Time Clock (with alarm) and an 8-bit Analog to Digital Converter (with tiny prototype area). I have dreamt up a few more, but have had very little (read no!) free time to do anything 6502 related in the past few months. Wich sadly also means my PAL-2 is still in the box it came in, unopened ....

[Ronny Ribeiro]

Very cool gadgets, Dimitri!

To view this discussion visit https://groups.google.com/d/msgid/pal6502/b9cf614a-462a-410c-9c15-c3f4521ab15an%40googlegroups.com.

[Kande Laber]

Did you write the driver software for these fine gadgets?

[GN Liu]

Very creative gadgets, Dimitri!!!

[Lars]

Hi,

I just found this post about PB6 as I build a simple LED Board and I miss one LED :-)

Does a list exist with all additional wires I need to add manually on a PAL-2 board Rev. 2.3?

Cheers

Lars

[Lars]

Ok, the two wires from above (PB6-U2, PB7-U3) are more "nice to have" features and not really needed, correct?

I understand PB6 (U3) to be used as an additional IO Pin at the Application Connector.

But what is the reason to have PB7 (U2)  at the Expansion Connector?

[Hans Otten]

PB7: To be able to add an audio cassette interface. 

And note the modification to add the Eduardo Casino RAM/ROM/FDC card.  

[Lars]

Thank you Hans :-)

[Lars]

Hi all,

I am currently using an small Add-On Board to Power my PAL-2, provide IOs and a RS232 Interface.

But I am not 100% happy with the layout and I like to change a few things like making the IO Connector compatible with the other expansions Boards.

I have asked the developer and got the permission to modify his design for my needs.

My version looks now...

Features:

J2 5V:
5V Input

J3 Serial-8:
Serial/Power Input from USB-Serial Adapter.

J5 RS232:
Serial In/Out with RS232 Voltage Level.

J4 I/O Port:
Provides Signals PA and PB from U3.
PB6* is added from Application-Connector Pin R.
See J6/JP3.

SW1 Power:

Power On the System from J2 (5V) oder J3 (USB-Serial).

On-Off-On Switch

SW3 Input:
Input via TTY (RS232/USB-Serial) or Keyboard.

SW4 TTY/Serial Mode:
Set Serial In/Out to use RS232 or USB-Serial.

SW5 (Top) or JP1/JP2 (Bottom):
Set the RS232 Sub-D Pins for Nullmodem or Straight 1:1 Cable usage.
Use Jumper or a DPDT Switch (SW5) at the Top or Solder Jumpers (JP1/JP2) at the bottom.

J6 (Top) or JP3 (Bottom):
Use Jumper J6 at the Top or the Solder Jumper JP7 at the Bottom to
connect Application-Connector Pin R to PB6* pin at the I/O-Port.

J7 Decode Enable:
Leave the Pins open which is the default setting.
Or you close the Jumper to give 5V/High Signal to the
Decode Enable Pin at the Application Connector.
Or you use the Pin "DecEn" himself and connect an external Signal.

I am not a professional PCB Designer but I am happy with the result.

Any thoughts? Maybe I did something wrong?

Cheers

Lars