LEGO Interface A (9750/9771) – LEGO Technic Control 1 (TC1) reference/ideas thread

[Bliss]

1 hour ago, Toastie said:

he output voltage is only 3.7V on my Int.A though. I guess that is in the normal range. So maybe using a tiny step-up converter and then feed the VIN line of the ESP32? There are the ESP32 Devkit1 boards with "5V" printed in the PCB pin; others have VIN printed, which can go to 9V and higher?

3.7 is not enough to power ESP32 board from its Vin.  the AMS1117-3.3 onboard regulator car take up to 15V but will heat too much at that voltage.  Even 9V is not ideal for long period of use.
Cannot plug directly to the 3.3v pins because the very max of ESP32 is 3.6V...
So yes a small MCP1700-3302E (looks like a transistor) would do the job and wire its output (3.3v) directly to 3.3v of ESP, not using the Vin pin at all.
You cannot plug both USB and 3.3v external power at the same time though or you have to use a Schottky diode (like a 1N5819) between the MCP1700 output and the 3V3 pin...
Also, using the Int.A "always ON" port you must use polarity protection like an Ideal Diode made with P-Channel MOSFET... 

Ideal ESP32 Devikit Vin voltage is 4.5 - 5.5 vdc using more will generate more heat in the AMS1117...  I would not go beyond 9v...  12v would definitly put the ESP32 at risk...

Anyway, plenty of DIY cheap solution to power a uController directly from the Int.A...

Edited 22 hours ago by Bliss

[evank]

Welcome @ryandesign. Your profile says you're in the US; whereabout? I'm in New Jersey.

I gave up on trying to learn assembly several years ago. I understand the concept, but I don't have a knack for programming this. I managed a hello world and decided to stick with BASIC. :)

Do you have any ideas for what you want to build?

I have tons of extra 4.5V motors but most of them are work out and sound terrible when you apply power. However the motors are easy to find. My problem is a shortage of touch sensors.

I have some extra 9767 cards, but the path of least resistance is to buy one of Jason Merrill's replicas. See www.blocko.net.

Edited 21 hours ago by evank

[Toastie]

1 hour ago, Bliss said:

So yes a small MCP1700-3302E (looks like a transistor) would do the job and wire its output (3.3v) directly to 3.3v of ESP, not using the Vin pin at all.

That would be my choice.

1 hour ago, Bliss said:

deal ESP32 Devikit Vin voltage is 4.5 - 5.5 vdc using more will generate more heat in the AMS1117...  I would not go beyond 9v...  12v would definitly put the ESP32 at risk...

That's true.

Thank you very much!
Thorsten

[amine]

48 minutes ago, Toastie said:

That would be my choice.

That's true.

Thank you very much!
Thorsten

In the Danish museum I just figured out LegoLines  has written CPM....

I don't understand very well what does it mean..

https://datamuseum.dk/aa/cpm/1b/1b8e2c0ec.html

Edited 20 hours ago by amine

[Toastie]

11 minutes ago, amine said:

I don't understand very well what does it mean..

Me neither 

I believe this some sort of description of the floppy disk format. The initial OS of the Piccoline was CPM-86 V3.1 = concurrent CP/M-86 if I am not mistaken. Many CP/M floppy formats are documented - in contrast to DOS, which was at the time always the same format? Well, I'm not sure. All I know is that the 22DISK DOS utility, which I used to copy Compis CP/M formatted floppies to DOS formatted floppies, has more than 370 such entries for as many computer systems running CP/M.

Best
Thorsten

[diegobaca]

On 8/6/2026 at 1:27 PM, diegobaca said:

@amine

Ok, so just to make sure I understand, these are the apps/emulators you're testing right now:

BBC Micro
B-em BBC Micro emulator for DOS:
https://emutopia.com/index.php/emulators/item/307-acorn-bbc-micro/102-b-em

Updated CWSDPMI.EXE for DOSBox compatibility:
https://www.delorie.com/djgpp/dl/ofc/simtel/v2misc/csdpmi5b.zip/

LEGO Lines BBC Micro disk/image:
https://www.mybbcmaster.nl/educ_lego.html

LEGO 9760 BBC Micro disk:
https://www.flaxcottage.com/Educational/software/LEGO/Data/Data_Download.zip

Apple II
Appler Apple II emulator for DOS (to test Apple II software I assume):
https://learn.adafruit.com/appler-apple-ii-emulator-for-dos/installation-and-setup

Is that everything you're currently testing, or are there any others I missed?

If you let me know which emulator + software you're trying, along with the links to download them, I can also help test on my side and see what we can get working with Interface A. 🙂

 

@amine

I looked into this properly because it's a great question. The short version is that hosting an Apple II or BBC emulator inside TC Logo Connect won't allow it to reach the Interface A as-is.

Why an emulator inside TC Logo Connect can't see the interface

TC Logo Connect presents the interface to DOS the same way the original 9771 ISA card did: as an I/O port at address 0x39D, which is the card's factory default and the address TC LOGO probes.

When a DOS program executes an x86 IN or OUT instruction on that port, the app forwards it over USB to the bridge and then on to the real Interface A. That single port is the entire connection point.

The Apple II, BBC Micro, and C64 communicated with the Interface A through their own connectors. As I understand it, the BBC used its User Port, while the Apple II used a card installed in one of its expansion slots.

An emulator recreates the computer, but it has no idea that the LEGO hardware exists. Inside the emulated machine, those connection points lead nowhere. When the LEGO software PEEKs and POKEs those addresses, everything stays inside the emulator. It never comes out the other side as traffic on the PC's I/O port, so there is nothing for TC Logo Connect to forward.

That's true for B-em, Appler, PC64, or any other stock emulator. Unfortunately, there isn't a change I can make on the TC Logo Connect side to solve this because the traffic never reaches it.

What could work

What would work is modifying an emulator that has its source code available so that its emulated User Port or slot card forwards the appropriate communication through IN and OUT at 0x39D.

At that point, it would simply look like another DOS program to TC Logo Connect, and the existing bridge to the real Interface A should work.

Sorry I couldn't be of more help with this right now. I may look into patching some of these other emulators in the future, as it would be really interesting to get the original LEGO software from these other platforms talking to a real Interface A through TC Logo Connect.

Cheers,
Diego

[evank]

>> As I understand it, the BBC used its User Port, while the Apple II used a card installed in one of its expansion slots.

@Diego that's correct. I assume there are one or more C64 emulators; that computer also goes through a user port.

[amine]

4 hours ago, diegobaca said:

@amine

I looked into this properly because it's a great question. The short version is that hosting an Apple II or BBC emulator inside TC Logo Connect won't allow it to reach the Interface A as-is.

Why an emulator inside TC Logo Connect can't see the interface

TC Logo Connect presents the interface to DOS the same way the original 9771 ISA card did: as an I/O port at address 0x39D, which is the card's factory default and the address TC LOGO probes.

When a DOS program executes an x86 IN or OUT instruction on that port, the app forwards it over USB to the bridge and then on to the real Interface A. That single port is the entire connection point.

The Apple II, BBC Micro, and C64 communicated with the Interface A through their own connectors. As I understand it, the BBC used its User Port, while the Apple II used a card installed in one of its expansion slots.

An emulator recreates the computer, but it has no idea that the LEGO hardware exists. Inside the emulated machine, those connection points lead nowhere. When the LEGO software PEEKs and POKEs those addresses, everything stays inside the emulator. It never comes out the other side as traffic on the PC's I/O port, so there is nothing for TC Logo Connect to forward.

That's true for B-em, Appler, PC64, or any other stock emulator. Unfortunately, there isn't a change I can make on the TC Logo Connect side to solve this because the traffic never reaches it.

What could work

What would work is modifying an emulator that has its source code available so that its emulated User Port or slot card forwards the appropriate communication through IN and OUT at 0x39D.

At that point, it would simply look like another DOS program to TC Logo Connect, and the existing bridge to the real Interface A should work.

Sorry I couldn't be of more help with this right now. I may look into patching some of these other emulators in the future, as it would be really interesting to get the original LEGO software from these other platforms talking to a real Interface A through TC Logo Connect.

Cheers,
Diego

It seems vice emulator have settings for handling the C64 user port and the PC serial com ports.

But I don't know if it can redirect the data from  one to another, probably not.

Edited 7 hours ago by amine