ZX Spectrum +2a / +2b (black) modification for D40/D80 cooperation
D40 and D80 are excellent floppy disk drives made by Didaktik. They were widespread in Czechoslovakia in past, but they are incompatible with 128k machines. This modification by Tritol is suitable for black ZXS +2.
Part list is very simple:
1 x slider switch
2 x 1k resistor
1 x 27C256 EPROM
1 x 74LS02
Modification: Cut /IORQ between CPU and GATE ARRAY. /IORQ from CPU connect to pin 12 of 74LS02, then connect pins 2, 3 and 13 of 74LS02 together. Connect pin 1 of 74LS02 to /IORQ on GATE ARRAY. Connect pins 10 and 11 of 74LS02 together. Pin 9 of 74LS02 connect to A5, connect pin 8 of 74LS02 to right pole of switch. Put 1k resistor between pins 8 and 7 of 74LS02. Connect +5V to middle pole of switch. Connect RA14 from GATE ARRAY through 1k resistor to left pole of the switch. Remove original EPROMs, burn 27C256 with +2 ROM or classic 128k ROM, bend pin 27 and put it into ROM-L socket. Connect that free pin 27 of EPROM to left pole of the switch. Then route /ROMCS to proper place on SYSTEM BUS connector. And that's it.