Ok, so the information in this post is pretty niche. I’m only aware of 4 of these computers in existence and currently none of them have the original remote control.
Mostly, this isn’t an issue because you can control the majority of the TV functions by the buttons on the screen. But ever since I’ve owned this computer, I’ve never found a way to switch to the scart input.
Over the last couple of years I’ve poked and prodded around to try and find out how the system works, through dissambling the DLL files I discovered that the computer and TV talk to each other using the I2C protocol. I also found that the 10pin connector that plugs into the riser board contains the SCL and SDA lines needed for the I2C protocol.
Today, I was having another play around and decided to hook up some wires and start sniffing the I2C bus to see if I could work anything out. The only issue is I forgot which pins they were! So I probed around and quite quickly found the SDA line, but wasn’t 100% sure which pin was SCL as none of them looked like what I expected and it had to be there.
I decided to hook up some dupont cables and just connect the known SDA wire and the ground wire, and then I would use the 3rd wire to go through each pin and work out which wire was SCL.
To do this, I would connect a wire, boot into windows and use one of the known “hot keys”, CTRL+ALT+T. This hot key tells the TV to switch to TV input, then you can use CTRL+ALT+P to switch back to PC.
This can also be achieved by pressing the two volume buttons together at the same time on the front of the unit.
This is where things happened that were VERY unexpected. Just using my 3 wires, I found the 3 pins where the hot key worked, so I must have located the SCL line. Great! But when I pressed CTRL+ALT+T a second time, the TV switched to the scart input!
What the hell! I pressed it again and it switched the AV2 which is the phono ports for composite input. Each time I pressed the key combination it cycled through the 3 inputs.
I really thought I’d gone mad. Surely all this time it wasn’t as simple as pressing the hot key multiple times? Somebody must have tried this! (Including me!)
I removed my jumper cables and plugged the original connector back in and booted up the PC. Pressed CTRL+ALT+T and it switched to the TV as expected, I then pressed it a second time and…….
Nothing! It just stayed on the TV channel. Something odd was going on.
I reverted back to my 3 dupont wires and once again I could switch inputs. So I then started connecting the remaining wires one at a time and testing the hot key. As soon as I reconnected the black wire, I was no longer able to switch inputs.
Without the black wire connected, the CTRL+ALT+P hot key to switch back to PC input no longer works, but you can still switch back to the PC by pressing the two volume buttons.
This was a very random discovery, and I’d love to take full credit for it, but it was pretty much blind luck that I stumbled onto this.
I do still want to investigate this further, as I am sure there is a shared memory address somewhere that if I configure a certain way it will send I2C codes to the TV. And now I can switch the inputs I want to capture the I2C commands and see if they are any different with the black wire connected vs not connected. But that can wait for another day now.
For the time being, I’ll just sit here and play a bit of Super Mario on my NES, hooked up to the PCTV via scart cable 😀
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