I've made GeoCart for C64/C128 and as you can see this cartridge is based on GeoAction project. All sources were rewritten and I2C bus is now in CPLD.

Hardware Info

On board:
1. XC9572XL
2. 512kB SRAM,
3. 256kB FlashRom
4. I2C RTC,
5. CR2032 3V battery


GeoCart can work in two modes, GeoRAM and RamCart. In expansion of RamCart mode you can switch this mode to extended.


georam.jpg GEORAM at beginning was a memory expansion made for GEOS, but now you can use it with game „Maniac Mansion” or with other tools
In GEOS you can use 512kB of memory expansion as virtual drive(s). Program CONFIGURE in GEOS can set one 1571 virtual drive or two 1541 drives.
GEOS disc with configure for GEORAM GEOSDISC

Ram Cart 2.5

Ram Cart is old Polish memory expansion cartridge, with 128KB RAM.
Main goals of this card are:
- GEOS support YTM GEOS
- virtual drive (7) with boot menu after reset Firmware
- macroassembler, install with load”*”8,1, ASSY
- burst copier BURST
In extended mode you have access to FlashROM so total memory in this emulation is max 768kB with 256B page/sectors. It's excellent mode to make virtual drive with solid content.


All modes can be set by dip switch.
1. Extended ⇔ Normal Mode,
2. GeoRam ⇔ RamCart,
4. RamCart read ⇔ RamCart write


GeoRam,NeoRam, BBram mode

$DFFE (write only)

bit (0 to 5) ⇒ address (8 to 13)

$DFFF (write only)

bit (0 to 4) ⇒ address (14 to 18)

RamCart Mode

$DE00 (write only)

bit (0 to 7) ⇒ address (8 to 15)

$DE01 (write only)

bit (0 to 2) ⇒ address (16 to 18)
bit (7) ⇒ 0 - Memory page at $8000 visible,


$FF Ram page memory.

I2C registers

In register $de02(RamCart mode) or $df02 (GeoRAM mode) there are only two bits:
bit (0) control of DATA line
bit (1) control of CLOCK line
Write to register
Bit (0) - 0 ⇒ DATA line is always ZERO you can read only ZERO from line
Bit (1) - 0 ⇒ CLOCK line is always ZERO you can read only ZERO from line
Reading from register
Reading status of DATA or CLOCK line is possible only if you set bit (0) or bit (1) to one.
Please visit Lee Davidson web page
I2C driver in assembler

projekt64/geocart.txt · ostatnio zmienione: 2011/08/12 22:47 przez kisiel
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