{"id":1559,"date":"2017-01-18T02:14:09","date_gmt":"2017-01-18T02:14:09","guid":{"rendered":"http:\/\/www.kernelcrash.com\/blog\/?p=1559"},"modified":"2019-06-14T08:11:17","modified_gmt":"2019-06-14T08:11:17","slug":"frankenstrad","status":"publish","type":"post","link":"https:\/\/www.kernelcrash.com\/blog\/frankenstrad\/2017\/01\/18\/","title":{"rendered":"Frankenstrad"},"content":{"rendered":"

So I bought the motherboard out of an Amstrad CPC-464<\/a>. This was like my Oric Atmos rationalisation<\/a> . It’s cheaper to just buy the motherboard of some of these old computers, rather than the whole computer (especially when I add in postage from the UK to NZ). And I am more into these old computers for my own curiousity and educational value, rather than just purely ‘collecting them’.\u00a0 In the case of the Oric, I came up with a Arduino based ‘PS2 keyboard to old-school key matrix’ converter to get around ‘not having a keyboard’.\u00a0 I was thinking of doing the same for the Amstrad, but I had a nice Cherry keyboard that I was given for free; ie. individual keyswitches and an easy single sided PCB. So I butchered it to turn it into an Amstrad keypad (well most of it).<\/p>\n

Yeah, I hate butchering things too … but it was gathering dust. Anyway, the CPC 464 service manual<\/a> has the matrix for the 464 on p11.<\/p>\n

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It was nothing like the existing wiring on the Cherry, so I initially cut every single PCB trace to a keyswitch, then ran a lot of wire wrap wires to make up the 464 matrix. Here’s the result<\/p>\n

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The Z70200 CPC 464 board I have has two connectors for the keyboard. One is a single row of 20 pins with 0.1″ spacing. But there are also two flex cable sockets which the original keyboard would have used. I soldered a pin header into the 20 pins, and then ran 19 (one pin is not used) jumper wires to plug into it.<\/p>\n

So I had a keyboard wired in. What about power and video output? I used a cheap LM2596 PSU (off ebay) and a 2.5A 12V DC plugpack to supply 5V, and connected it in on the right of the board via the cassette connector (CP001). For video, the 464 has a DIN socket on the back that pumps out RGB and sync. This is 15KHz\/50Hz style RGB, so I just created a straight through cable from the DIN to a VGA plug, then plugged this into the input of my Gonbes (which has an ATTiny85 hooked up as per here<\/a> ). And I powered on, and all was good (well I had one or two mistakes in my keyboard wiring, but after I fixed those then it was all good);<\/p>\n

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What about loading stuff? The 464 had a built in cassette recorder. I did not have the cassette unit at all. There’s a few links online about how to run an audio AUX-IN input in your 464. Most seemed to run wires directly in to spots on the circuit board that is part of the cassette player mechanism. I did not have the cassette player at all. If you look at the cassette connector on the main motherboard, the cassette read\/write connect directly to the 8255 IO chip with no buffering\/amplification.<\/p>\n

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I will also note here that there are a few different versions of the above. Maybe there are a few board designs. My Z70200 board matches the above. But the actual service manual seems to have a slightly different diagram with GND and +5V on different pins. ‘RD DATA’ is what we’re interested in so far as cassette loading.<\/p>\n

I tried a few different simple transistor amp circuits, but ended up with the following<\/p>\n

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The LED attached to the motor control is so that you can see when the Amstrad (thinks it) has activated the cassette motor. For most games I found the motor LED is on continuously while loading, but there are a few that\u00a0 you’ll need to pause the audio when the LED goes off temporarily.<\/p>\n

And now I can enter<\/p>\n

run””<\/p>\n

and load a game into the thing. Here it is running ‘Betiled’<\/p>\n

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I am new to Amstrad-land (I had never used one before, nor tried an emulator!), so I had to figure out how to load cassette images. For me this was;<\/p>\n