This is information about a FPU board I made for my Apple IIe.

I do that because I want one usable with DOS 3.3 and with CPM + Z80 Softcard. The one made at the Apple II time (like CCS 7811) dont work with the Z80 Softcard...

They use AMD AM9511 / Intel C8231.

If you dont use interrupt (I mean if you dont have a routine that manage the interrupt) leave the INT J2 jumper open.

J4 must be put to GND (as on the picture).

The board can be set for 4 MHz clock or 2 MHz clock (J3 jumper). Usually AMD --> 2 MHz, INTEL --> 4 MHz but double check the exact reference of your FPU.

It is largely inspired from the Microcrunch from John Hart (see pdf above).

Have fun !

20/06/2023 Philippe Roehr