W65C02SXB to PAL-1 conversion

[Stefan S]

Hello friends,

I got a WDC W65C02SXB SBC board https://wdc65xx.com/Single-Board-Computers/w65c02sxb/
and would like to convert it to some PAL-1 like board.
My plan is to remove U10 74HC138 and add the missing chip selects to the XBUS_02 connector. As everything is quite tiny the easiest way to pickup or better inject the missing chip selects signals is to connect wires to the status LED resistors.

The idea is to plug an adapter board onto the XBUS_02 connector which does the address decoding in a PAL-1 way and converts the pinout from XBUS_02 to PAL-1 Expansion bus.

As you may have noticed the W65C02SXB does not have any RIOT chip but it has two 

W65C22 and one W65C21.

One of the W65C22 (U5) is used for the USB port so cannot be used.

My idea is to replace the main RIOT with the W65C22 (U3).

If I invert A1 and swapped it with A0 before I feed that into RS1 and RS0 of the W65C22 the 4 IO-Registers are in the same order as they are on the RIOT that leaves the timer incompatible.

The system RIOT timer is used by the KIM-1 ROM only for delays in the tape routines what could be patched.

I have no idea if there is any software that either reprograms the system RIOT timer or reuses the delay routines used for tape.

I have some ideas to recreate the RIOT Timers with less then 10  74-series TTL chips if needed.

What do you think about that?

Stefan

[Hans Otten]

As it is an 6502, it may work.
The challenge will be to write a KIM-1 compatible ROM. At least the most used entry points have to be  stay at the same location and return the same results (like changed registers).
Are you planning on adding the LED display and keypad? That will require hardware identical to the KIM-1/PAL-1/PAL-2.

Or just serial bitbanged TTY?  Fewer hardware components, but beware the echo trick requires some logic ICs. And a system clock of 1 MHz.

[Kande Laber]

Maybe you are a great expert and this will would be an easy project for you.

But in my opinion it would be far easier to ask Liu Ganning to resume the production of the PAL-1 and to order one subsequently.

On Sunday, March 23, 2025 at 7:00:19 PM UTC+1 szi...@gmail.com wrote:

[Stefan S]

Hello Hans,

the 74HC138 is removed to add a new mapping that replicates the KIM-1 memory map.

For the first tests I would build an address decoder as in KIM-1 later use a CPLD (so far don't have experience with CPLDs)

Yes, a keyboard display unit is planned.

PHI2 system clock is 8MHz plan is to make it switchable with the dividers 1, 2, 4 and 8.

The ROM-routines should work out of the box as the registers of the VIA IO-part are matched to RIOT IO-part.

PCB contains as 65C51 but that would require some more ROM patching as I would like to do.

Stefan

[Stefan S]

After thinking about that, an unpopulated PAL-1 or PAL-2 board could make things easier.

I would be also interested in broken boards I would not mind about some ripped of traces or solder pads.

I would need adapters to convert from PLCC to DIP but could use all the chips from the W63C02SXB just not the RAM as it is soldered directly.

Also the design files would be of interest to me as I could do a PLCC version and other changes when my idea with the VIA instead of RIOT works out well.

Of course I could create my own design based on the schematics but that would consume a lot of time.

Stefan

[Hans Otten]

Be sure to look at the logic circuits around TTY and audio cassette interfaces. They are essential to replicate.

[Stefan S]

that is why I selected the PAL-1 or PAL-2 and not the KIM-1 as reference.

[Stefan S]

http://retro.hansotten.nl/wp-content/uploads/2021/11/E29qKBEUYBA781I-scaled.jpg
For me tape is not important in the beginning, but plan is to use this: http://retro.hansotten.nl/uploads/pal1/Cassette_expansion_manual.pdf