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PIC18F87J50 with external RAM reference design

Former Member

I need a (relativly) cheap "old school" CPU with external memory for executing programs loaded of a SD card, with a little OS running at boot for the basic IO.

 

The PIC18F8 family can run in "Microprocessor mode", which turns the chip into a soaped up Z80 that have a 2 MB address space. App note for reference: http://ww1.microchip.com/downloads/en/AppNotes/00869b.pdf

 

I've read the datasheet and tried to search for a reference desgin that hooks up the PIC to external parallel SRAM, but I cant find any.

 

If any PIC wizards are out here, can you confirm that my interpretation of the Microprocessor mode indeed gives me a more general purpose CPU with a 2 MB address space ?

 

Bonus question, any advice on a parallel SRAM for the in the heading mentioned PIC ?

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  • 0

    Why not use an ARM Cortex, ST have parts with 200k bytes of RAM and an SD card interface - so you could run your code in on chip RAM (unless it's huge.) Another trick you could try is to copy the code into on chip flash - this would work with quite  a few different processors and certainly can be done on the ST  Cortex parts (STM32F4xx might be the best parts to start with.)

    The external memory interface on the PIC seems very clunky (there are PIC32 bit parts with much better memory interfaces I think)

     

    MK

  • 0 in reply to michaelkellett

    I'm planing to build a small retro computer with a small dos like OS with the ability execute user programs loaded from SD card, I've looked at parts like the Z80180 and the 16 bit version of the 6510 but they all fall short in the tooling area, I need around 2 MB flat address space and a resonable fast (but not to fast) cpu that can be connected to my (FPGA based) graphics subsystem. Its complicated yes, and mostly controlled by not-so-rational arguments, but if I just wanted something fast, I probably by a Pie and be done with it.

  • 0 in reply to Former Member

    Hi,

    If you want to simplify the electronic schematic, use a PIC32MZ2048ECM100 which has 2MB flash and 512KB RAM. No external component needed ;=)

    In this architecture you can execute code from internal flash or internal ram. You can also run it at a lower frequency than its nominal frequency (200MHz) to reduce power consumption. You can debug it with a Pickit3 but maybe you don't need i if you use a PIC32MZ embedded connectivity starter kit which has on-chip debug.

    there is even an Arduino based on this PIC32MZ 200MHz called Chipkit Wi-Fire

    Regards

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  • 0 in reply to Former Member

    Hi,

    If you want to simplify the electronic schematic, use a PIC32MZ2048ECM100 which has 2MB flash and 512KB RAM. No external component needed ;=)

    In this architecture you can execute code from internal flash or internal ram. You can also run it at a lower frequency than its nominal frequency (200MHz) to reduce power consumption. You can debug it with a Pickit3 but maybe you don't need i if you use a PIC32MZ embedded connectivity starter kit which has on-chip debug.

    there is even an Arduino based on this PIC32MZ 200MHz called Chipkit Wi-Fire

    Regards

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