Memory Card: Revision A

Memory Card: Revision A

Last Updated: November 09, 2005 09:48:34 PM

Revision A of the memory card with the RAM installed at 0x0000 – 0x7FFF and the EPROM at 0x8000 – 0xFFFF. The jumper blocks on the left enable and disable 4K memory blocks. This card has RAM 0x0000 – 0x6FFF and EPROM 0x8000 – 0xEFFF areas are enabled.


The memory card contains 64K of RAM and 64K of EPROM made up four 32K x 8 chips (2 RAM, 2 EPROM). The RAM and EPROM are each spread across the entire 64K address space of the 1802. Each 4K block of RAM or ROM can be separately enabled or disabled by one of four jumper blocks, each RAM and EPROM chip has a separate 8 x 3 jumper block. Of course any 4K block can only be occupied by either one of RAM or EPROM. The card was designed with this flexibility to accommodate old software of my own and new software such as ELF/OS. The card replaces the original System-4 16K Ram card.

NOTE: This was the first new card built for System-5 and although the first design and layout worked, Rev-A of the card, has a few simple flaws (no bypass capacitors) and is missing a few features and standards I decided each System-5 card should conform with.

Issues/todo log

Date Description Status
Dec-20-2005 Add bypass capacitors Done Rev B
Dec-23-2005 Update bus connector – Fix labels and hole size Done Rev B
Jan-12-2005 Add Power and Status LEDS Done Rev B
Jan-23-2005 Add card name and version label Done Rev B
Feb-12-2005 Add label information to jumper block silk screen Done Rev B
Mar-05-2005 Convert jumper blocks from separate GND and VCC for each block location to a pull up resistor and GND jumper for each block. Combine jumper selection block

for each 32K RAM/EPROM pair.

Done Rev B

Schematics, board layout, and operational description

Revision Production Date Schematic Layout Operational Description
A Dec-16-04 mem3.sch mem3.brd Rev. A ops notes
B Current Development Board


mem3-b.sch mem3-b.brd Rev. B ops notes