Interfacing CPC with a microcontroller

[revaldinho]

It needs to be considered that the I/O pins of the Pico must be 5V first, otherwise the Pico could be damaged by direct connection to the CPC.

Yes, a common problem with the modern CPLDs/FPGAs and MPUs. It would be nice if there were more parts with 5V tolerance available, and I am still sorry to have seen the demise of the XC9500 5V PLCC parts, but there are easy solutions given that you need to do a PCB to mount the part on the CPC anyway.

[Richard_Lloyd]

Hello all. As I don't have the necessary 'heavyweight' electronics skills, I've been approaching this topic using existing hardware.


First I built one of revaldinho's CPC-Ker-Plink co-processor cards and then installed a Raspberry Pi Zero WH along with a Waveshare USB/Ethernet HAT. This week I've been checking it co-exists with my other add-ons - so far so good.


It all went together without any problems and the photograph shows it on an expansion backplane with a memory card and FlashGordon. Now giving some thought about how to utilise SD Storage, 3 USB ports, WiFi and Ethernet.


I have some spare CPC-Ker-Plink PCBs.


Cheers.

[eto]

It needs to be considered that the I/O pins of the Pico must be 5V first, otherwise the Pico could be damaged by direct connection to the CPC

The GPIO of the Pico seem to be 3.3V only. I guess that makes it a lot harder to connect it to the CPC then, right?

"The Raspberry Pi Pico's GPIO is powered from the on-board 3.3V rail and is therefore fixed at 3.3V"

[revaldinho]

The GPIO of the Pico seem to be 3.3V only. I guess that makes it a lot harder to connect it to the CPC then, right?

It's definitely less convenient.


I use 74LVC245s for level shifting on my CPLink boards. These are cheap, readily available in 20 pin DIP packages and good for through-hole PCBs and breadboarding. If building PCBs then a large subset of 74 series logic is available in the LVC family in SMD packages as well as these octal transceivers. In fact it you're happy with SMD soldering then there are a huge number of options here - this is what a quick search on Farnell shows up.


For breadboarding, you can find breakout boards using MOS based auto-sensing level shifter chips at many of the usual suspects, including

   
• sparkfun-level-translator-breakout-pca9306-1
• sparkfun-logic-level-converter-bi-directional
• Adafruit 4 channel converter
• Adafruit 8 channel converter

I haven't tried any of these myself, but I think I have a couple here ready for experiments at some point. The real kicker is that these breakout boards are actually more expensive than the RaspberryPi Pico itself individually, and you're probably going to need 2 or three of them. At least in a breadboard they are reusable.


Aside from that you have any number of options of simple current limiting series resistors, potential dividers, or resistor-diode and resistor-transistor shifters.


So, it's all a bit of a pfaff but the Pico can still be an alternative to CPLD/FPGA based hardware design and very nearly all of those chips are also 3V3 only these days too.

[ajcasado]

Any interest here in using the new RaspberryPi Pico as a CPC programmable peripheral ?


Programmable state machines for bit banging on IO pins independently of the two 133Mhz dual cores, looks interesting. And they certainly are cheap.

I guess that a VGA external card for the CPC should be possible. There is SIO code for VGA output and enough SRAM. Things as double-buffering, hardware sprites, hardware scrolling, 2D and 3D drawing hardware acceleration also could be done.