July 25, 2025, 04:24:26 PM

Neo6502 / Serial Access

Started by mscha, June 28, 2025, 11:48:29 AM

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mscha

Has anybody successfully established a serial connection from Windows to the Neo?
I tried it with the MOD-USB-RS232 card - no success.

LubOlimex

Describe what does it mean "no success"? Nothing displayed on the terminal upon power up or what?

Is this with the default firmware that the board arrived?

Are you using the ribbon cable between MOD-USB-RS232 and the Neo6502's UEXT connector? Or jumper wires?

Did you change any jumpers on MOD-USB-RS232 recently or in the past? You should revert any changes. All jumpers should be as per default.

Is the MOD-USB-RS232 properly recognized in your operating system? Maybe try re-installing the drivers, point manually the entry to the mchpcdc.inf file inside this archive:

https://www.olimex.com/Products/Modules/Interface/MOD-USB-RS232/resources/Demo_MOD-USB-RS232.zip
Technical support and documentation manager at Olimex

mscha

The Neo showed up as COM4. I used PuTTY to connect. But no reaction to my typing.
- Default firmware used
- Ribbon cable used
- No jumpers changed
 

LubOlimex

I tested it today. It appears to be working. Here is what I did:

1. Got Neo6502 from the shop
2. Got MOD-USB-RS232 from the shop

Didn't change anything both hardware-wise and software-wise in either board, nor I plugged anything in either board.

3. Got USB mini cable and USB C cable - the first to connect the USB-RS232 board, the second to power the Neo6502 board

4. Connected MOD-USB-RS232 to a mini USB cable, it created a COM port in my computer and I inspected the COM port number from "Windows Device Manager". It is COM8 here.
5. Opened a terminal on COM8 with 115200 board. I used puTTY software.
6. Then connected the UEXT cable between the MOD-USB-RS232 and the Neo6502.
7. Finally connected the USB C cable to the Neo6502 to power it.

Got two lines after boot, which is a sign that the hardware setup works fine and I get data on the serial at the UEXT:

Configuring DVI
Core 1 start



This is my hardware setup:



Try the same steps. It is important to power the Neo6502 last.
Technical support and documentation manager at Olimex

mscha

Thanks.
I did all this in the same order. The only difference: the board shows up as COM4 on Ports (COM & LPT).
Then,

UEXT test ERROR!
UEXT test ERROR!
UEXT test ERROR!
UEXT test ERROR!
UEXT test ERROR!
UEXT test ERROR!
UEXT test ERROR!
UEXT test ERROR!
UEXT test ERROR!

LubOlimex

It is still good message which means the hardware setup is fine. The reason we get different output form the board is probably different firmware was loaded somehow at your side. It is easy to recover via the USB type A to A cable. Try updating the firmware as explained in chapter "Programming RP2040" on page 12 of the manual here:

https://github.com/OLIMEX/Neo6502/blob/main/DOCUMENTS/Neo6502-user-manual.pdf

Try with both the suggested files "apple2e-5.uf2" and "apple2_800x600_400MHz.uf2".

To program the .uf2 files you need USB A to A cable.
You disconnect the power supply USB-C cable, then press the BOOT button and plug the USB-A cable to USB host connector. Your computer will show a new drive. Once this new drive shows copy the .uf2 file to it. Once the firmware is programmed the drive will disappear. This means the RP2040 now has the new firmware loaded.

After the update test if you get similar to mine message over the serial.





Technical support and documentation manager at Olimex

mscha

I also have a Neo6502pc with Apple //e firmware.
Tried the same approach with it and received:

Configuring DVI
Core 1 start
MSC mounted, inquiring
MSC 7632MB SanDisk Cruzer Facet rev 1.00
Error 4 opening file ProDOS_2_4_3.po

Then no more reaction. Don't know what it means.

 

LubOlimex

It means that the serial communication that was the original problem is now fixed. There is serial output coming from the boards.

It is another problem that if you want meaningful interaction over the serial you should upload software that handles that. The software we place on these boards is meant to work over HDMI and it only prints some debug info over the serial to demonstrate that it works. What exactly do you expect to happen? Do you expect the serial to copy the HDMI?

Maybe read here:

https://neo6502.com/wiki/Serial-Interface/
Technical support and documentation manager at Olimex

mscha

On the neo6502, I have David Given's cpm65 installed. And I want to use the serial interface to access cpm65 with its 6502 assembler 'asm' from my laptop. Otherwise, I have to switch a USB stick from one computer to the other, including 'eject' and restarting the neo for each debugging step.   

LubOlimex

I am not sure if the config in that project is set to the pins we use for serial output. We use GPIO29(RX) and GPIO28(TX) for the serial and original Neo6502 uses GPIO25 (RX) and GPIO26 (TX). Worth checking and asking at the GitHub.

The project otherwise should work fine under HDMI, I am just not sure if the serial pins have been edited. I know David and Paul did work to add support for the Olimex board. It is advertised in the beginning like the Olimex board is supported. Did you follow the advice at his GitHub, there is section for neo6502:

https://github.com/davidgiven/cpm65?tab=readme-ov-file#nano6502-notes
Technical support and documentation manager at Olimex