Dragon Shared Memory

Board for share data and/or programs between a PC and Dragon Computer throw expansion bus.

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The aim of this project is design a board for share data and/or programs between a PC and Dragon Computer throw expansion bus. Using a 2K x 16 Dual-Port SRAM chip attatched to Dragon computer expansion bus and attatched to external AVR microcontroller for interact from PC and read or write data/programs to Dragon.

Other purposes can reach a development card used for test programs developed with 6809 compiler directly to read hardware same as Dragon 32/64.

Alpha version (Prototype)

Its divided into two cards.

Dragon Memory Card

This card contains a Dual Port SDRAM Chip connected directly to Dragon Computer expansion bus. And can accessed directy from Dragon Computer from address $C000. 

USB Data Transferd Card

This card contains ATMEGA8515 microcontroller and Latch 74HC573 for attach DP-SRAM as a external microcontroller RAM. 

This version serial works at 300 baud.

Beta version (Manufactured PCB)

The first single PCB board that contains all Memory+Data transferer. PCB are manufactured by PCBWay and designed with KiCAD.

Firsts test are go well, but I needed ajust SUT_CKSEL  to Ext. Crystal/Resonator High Freq; Start-up time: 16K CK + 4ms  and activate BODEN and CKOPT. (FUSES: 0xC1, 0xAF). This is a important note because other timming configuration not works very fine with this type of external RAM.

Finally adjusts serial speed to 9600 baud.

Schematics, PCB and Gerber files made with KiCAD.

x-zip-compressed - 1.03 MB - 06/26/2019 at 01:13


  • 1 × IDT 7133SA 2K x 16 DUAL-PORT SRAM
  • 1 × ATMEGA8515L Microprocessors, Microcontrollers, DSPs / ARM, RISC-Based Microcontrollers
  • 2 × 74HC00 Electronic Components / Misc. Electronic Components
  • 1 × 74HC573 Electronic Components / Misc. Electronic Components
  • 1 × FTDI USB-TO-TTL Serial converter

View all 7 components

  • New PCB design

    Tomeu Capó06/26/2019 at 01:27 0 comments

    I redesign project hardware board to single PCB and test first PCBWay manufactured board version successifully.

    Also reduced PCB board size and upload latest schematics, PCBs and gerber files to project files.

    This new board includes FTDI chip directly on same board and I put pull down resistor array on I/O unused RAM ports.

    Now I solve bugs into AVR microcontroller firmware to work with external RAM, and create a simple C# PC program to send any data to RAM.

  • Make better use of memory space

    Tomeu Capó09/02/2017 at 18:50 0 comments

    Improve memory addresses

    Make better use of the address space to increase the capacity of the solution. We currently only use the lower bytes of each memory location.

    IDT SRAM Chip have 16 bit data bus, and now only use first byte. Can multiplex data on the same chip address but get @13 or @11 for detect change byte for R/W.

    Meanwhile I testing data transfer with MCU and Dragon Computer:

View all 2 project logs

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