Laptop Desktop N C D25 D25 U A 1 1 L B 2------3 L L 3------2 | E /-4 4-\ M \-5 5-/ O D25 /---6 6---\ D T | 7------7 | E O | 8 8 | M D25 \--20 20--/ N C D25 D9 U A 1 1 L B 2------2 L L 3------3 | E /-4 4---\ M \-5 /--5 | O D25 /---6 | 6---/ D T | 7---/ 7-\ E O | 8 8-/ M D9 \--20 9 Desktop WP-2 N C D9 D9 U A 1 1 L B 2------3 L L 3------2 | E /---4 4---\ M | 5------5 | O D9 \---6 6---/ D T /-7 7-\ E O \-8 8-/ M D9 9 9 N C D25 D9 U A 1 1 L B 2------2 L L 3------3 | E /-4 4---\ M \-5 /--5 | O D25 /---6 | 6---/ D T | 7---/ 7-\ E O | 8 8-/ M D9 \--20 9 |
First, you need to cross-pin two sets of pins on each connector. This lets the respective computers take care of their own timing requirements.
Second, you connect a 3-conductor wire between the two connectors.
What I am not showing you is how to strip and tin the wires, solder the parts and put on the hoods. But those items are minor to getting the wires connected correctly.
The Original Laptop Computer . . . 1983