The Microtan-R boards already provide a full complement of memory for new systems but do not provide an option for expanding an original system. Original boards are unobtainable so I decided to design a new memory expansion board.
The board replicates the functions of the Tangerine Users Group 64K RAM board and so as well as the main memory it also provides the other two features of that board. Firstly, the ability to overlay any of the TANEX EPROMS such as the BASIC EPROMS with RAM, and secondly the ability to overlay the 7K of RAM provided by 14 x 2114 devices on TANEX should these devices become faulty.
With modern components all of the functions could be implemented in a small part of an FPGA, or a single SRAM device and a CPLD. For this board I decided to stay with 1980s technology so it uses 6264 DRAMs and 74LS logic.
The manual can be downloaded below. The board was designed in KiCad and if anybody would like the designs get in touch and I will be happy to provide them. I have some spare PCBs if anybody would like to purchase one please get in touch.