IMG 6319

The Ultimate 1MB is an "almost solderless" install. Four lines still need to be soldered, and they can all be taken from the CPU.

On a 1200XL this is socket U21. The four lines needed are:

PHI2 (pin 39)

RW (pin 36)

RESET (pin 40)

HALT (pin 35)

On a 1200XL we also need Pin 23, which needs to be connected to the top pad of jumper W6. This is needed to complete the ROM upgrade.

In this image we see the underside of the 1200XL board, with tap points for the four pins needed. I dislike soldering directly onto chips, so trace the lines until I find a suitable tap point. See the next image for annotation.