Sardis Technologies ST-2900 RAM-512 Board

(This page is still under construction.)

The ST-2900 RAM-512 board is an expansion board that plugs into the ST-2900 CPU board to provide 512KB of extra RAM, typically used for a RAM-Disk or a printer buffer.

RAM-512 board features:

• 512KB (or 128KB) memory using 16 256Kx1 (or 64Kx1) DRAM chips
• 128 (or 32) 4KB pages, mapped into the $E000-$EFFF area one page at a time
• two RAM-512 boards can co-exist in a system, for a total of 1MB
• fully transparent DRAM refresh
• uses a delay line for reliable and precise timing
• RAM-Disk software drivers for FLEX and OS-9 Level I operating systems
• two 60-pin connectors plug into CPU and FDC boards
• only 4.3"x6.3" (110mm x 160mm), 2-layer board with soldermask and silkscreen

(The new NVRAM/RTC board will have 34x the capacity, yet will be smaller and cost less to build.)

Once I had built and installed a RAM-512 board in my main ST-2900 computer system, I was hooked! It was so much quieter, faster, fewer floppy disk swaps, less wear and tear on the floppy disks and drives, etc. It was bliss! Fortunately I lived in an area where power outages were rare, so I left the system powered up 24/7 and usually didn't lose any data for half a year or more. (Of course I backed up the RAM-Disk contents frequently, just in case.)

One of my industrial customers paid me to write custom software to allow using an ST-2900 CPU and RAM-512 board set as a large printer buffer.

The RAM-512 board is slightly larger than the CPU or FDC boards, to allow for two 60-pin connectors. At the time I designed the board I couldn't find an appropriate stack-thru connector (like the PC/104 bus used 2 years later), or at least not one that was affordable.

The RAM-512 board was announced on page 48 of the September 1985 issue of '68' Micro Journal, and reviewed on page 16 of the June 1986 issue.

Pictures of bare board (1.1MB .jpg) and assembled board. (??-??KB .jpg)
PCB artwork. (176-225KB .png)

	ST-2900 RAM-512 Hardware and Software User's Manual. (4.4MB .pdf scanned image)
	Other notes for the ST-2900 RAM-512 board. Includes addendum/errata to the manual, etc. (not available yet) (??KB .txt)
	DSK image (35T/SS/SD FLEX format) of FLEX drivers for ST-2900 RAM-512 board, as distributed. Also includes bootable version of MEMTEST. (not available yet) (??KB .zip)
	DSK image (35T/SS/SD FLEX format) of source code of FLEX drivers for ST-2900 RAM-512 board. (not available yet) (??KB .zip)
	DSK image (35T/SS/DD CoCo OS-9 format) of OS-9 Level I drivers for ST-2900 RAM-512 board, as distributed. (not available yet) (??KB .zip)
	DSK image (35T/SS/DD CoCo OS-9 format) of source code of OS-9 Level I drivers for ST-2900 RAM-512 board. (not available yet) (??KB .zip)