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The P8X180 Computer System — Parallax Forums

The P8X180 Computer System

Hello,

Presenting the P8X180 Computer System.

This is a Single Board Computer (SBC) based on the Zilog Z8S180 8-bit microprocessor, with the help of two Propeller 1 microcontrollers driving the onboard peripheral interfaces.

The main board includes the device interfaces needed to run stand-alone such as VGA video, USB or PS/2 keyboard, mass storage, and others. Four slots allows to expand the system with additional peripherals such as modems, printers and hard drive controllers.

Specifications

  • Z8S180 (Z180) CPU @ 18.432 MHz
  • 512 KB flash ROM
  • 512 KB static RAM
  • 256 colors VGA video
  • USB and PS/2 keyboard
  • Dual channel audio
  • SD Card Storage
  • 1 Full TTL serial port
  • 1 Simple TTL serial port
  • I2C and SPI interfaces
  • Battery-backed Real Time Clock (RTC)
  • 32-bit floating point math co-processor
  • 4 expansion slots

The project is completely open source. Design files, firmware and software sources are available from the the git repository.

Reference links:
https://www.maccasoft.com/electronics/p8x180-motherboard/
https://dev.maccasoft.com/p8x180

Enjoy!

Comments

  • Neato!

    Are these expansion slots to any particular standard or custom?

  • maccamacca Posts: 323

    The pin disposition is custom, the connector type is "incidentally" the same used by the ZX Spectrum (2x28 pins, less the cut sides).

  • Very impressive. Are you using this board now? And how did you make the circuit board and connect all the peripheral devices? I always wondered how that is done.

  • maccamacca Posts: 323

    @Ludis said:
    Very impressive. Are you using this board now? And how did you make the circuit board and connect all the peripheral devices? I always wondered how that is done.

    Yes, I'm using it.
    All the schematics and PCB layout are available from the links on the first post. Feel free to ask if you have questions.

  • What software did you used to make the schematics?

    I'm new to this and I noticed your battery negative terminal is connected to ground and positive connected to an IC. I'm working on a clock that uses an RTC with a battery and had a question. If you loose power the battery can still discharge to ground. I wondered if, you disconnected the ground by unplugging the whole device, would the battery have a ground so that the device could keep operating on the battery? What does your circuit do?

    I had unplugged my clock for a few days and the time wasn't kept, but I plugged my clock in later and did some tests and the battery seemed to be working fine when I had ground connected.

  • maccamacca Posts: 323

    @Ludis said:
    What software did you used to make the schematics?

    KiCad https://www.kicad.org/

    I'm new to this and I noticed your battery negative terminal is connected to ground and positive connected to an IC. I'm working on a clock that uses an RTC with a battery and had a question. If you loose power the battery can still discharge to ground. I wondered if, you disconnected the ground by unplugging the whole device, would the battery have a ground so that the device could keep operating on the battery? What does your circuit do?

    I had unplugged my clock for a few days and the time wasn't kept, but I plugged my clock in later and did some tests and the battery seemed to be working fine when I had ground connected.

    Not sure to follow. The battery is needed to keep the RTC date and time when it is not powered, it doesn't power anything else.

  • LudisLudis Posts: 45
    edited 2021-05-10 21:56

    @macca said:
    Not sure to follow. The battery is needed to keep the RTC date and time when it is not powered, it doesn't power anything else.

    If you had the RTC floating (not grounded) with the battery connected. Would it still run the RTC? I thought your schematic showed the negative side of the battery connected to ground and not the ground on the RTC. Nowhere for the current to go to if the battery negative was not connected to ground on the RTC. I hope that makes sense.

    Thanks for software I will use that to make a schematic for my project! Will be posting soon. Stay tuned for the digital clock.

  • maccamacca Posts: 323

    @Ludis said:
    If you had the RTC floating (not grounded) with the battery connected. Would it still run the RTC? I thought your schematic showed the negative side of the battery connected to ground and not the ground on the RTC. Nowhere for the current to go to if the battery negative was not connected to ground on the RTC. I hope that makes sense.

    Still, don't follow, the battery is connected to ground as the RTC (pin 4 of IC11).

  • Ok I see it is connected to the RTC ground. nvm. thanks

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