Tony wrote: If my eyes read it correct, the RAMs are DEC 85S68. A Google search shows that it was made by National Semiconductor and that it is a 64-bit static RAM. My eyes are still good :-) I did not find a datasheet, unless you order and pay for it! The schematic is clear enough to figure things out ... - Henk, PA8PDP. This message and attachment(s) are intended solely for the use of the addressee and may contain information that is privileged, confidential or otherwise exempt from disclosure under applicable law. If you are not the intended recipient or agent thereof responsible for delivering this message to the intended recipient, you are hereby notified that any dissemination, distribution, or copying of this communication is strictly prohibited. If you have received this communication in error, please notify the sender immediately by telephone and with a "reply" message. Thank you for your cooperation.