Hi Steven Here is what Barry Watzman just sent me: ********************************************** "A jumper is required between the center pin of JJ503 and Pin 17 of P509, or P4 of WH-88-16 (which connects to Pin 17 of P509)." On some models the jumper was factory installed by soldering on the back of the CPU board. Barry Watzman ********************************************** Also, you should joint the mail list sebhc. It speicalizes in H8, H89 and H/Z90 stiff. It does a little talking about Z100's and H11's but it is just talk. Hope this helps. I was a little late for the floppy controller. Dwight see: www.sebhc.org