From: Jarek Adamski Date: 2003-05-03 06:34 The PL3MEM is my recent interface project. Overview. This is quite simple and cheap. Designed for small box - 105mm x 55mm. It works like ZX+3, what means 16kB switching in section A done with bit 4 in #7FFD port and bits 0, 1 and 2 in #1FFD port. The IDE is controlled by 8255 in ports #1B, #3B, #5B, #7B. Software. The ZXVGS P3M can be used on it and probably the +3e will work, too. Bit 1 in #1FFD port selects the mode: 0 - four ROM banks, 1 - two ROM banks with TRETRAP and two SRAM banks. This bit can be changed only when bit 2 goes from low to high (so outing #00 to #1FFD port doesn't change it) and is set while reset (to start from BOOTROM). bits bit 4 in #7FFD in #1FFD 2 1 0 0 1 ------------------------- 0 0 0 ROM0 ROM1 1 0 0 ROM2 ROM3 0 1 0 BOOTROM ZXROM (TRETRAP active) 1 1 0 DOSRAM SYSRAM X X 1 interface disabled ZXVGS P3M uses mostly the SRAM - is loaded from the HDD. In the EPROM there are only some BIOS procedures, that don't require frequent upgrades. The +3e uses mainly the EPROM only. In case there's no +3e, the 64kB ROM can be used as ROMDISK and contain ZXVGS utilities or other software. Hardware. The base construction is ports decoder, port latches, 32kB SRAM, 128kB EPROM and 8255 for IDE. (The 8255 could be replaced with set of wires to have +3e simple IDE, but this doesn't make sense IMHO.) In case the EEPROM is used, the ROM0, ROM1, ROM2 and ROM3 can be reprogrammed inside interface. The other 64kB cannot due to presence of TR-DOS traps. The 256kB or 512kB chip has also limited sense.