I got my new dual parallel port today, so I spent the evening updating the Plus/4 downloader to allow me to change port address, and writing the new C64 downloader. The piccy shows the new cable before I've tidied it all up and put the casing on; but now that I know it all works, I can do that whenever.
The C64 cable is cool as it sets a whole byte at once (unlike the +4 that sends nibbles). But it only seems to match the +4 speed, probably due to the higher clockspeed on the +4. I suspect I could knock a second off the +4 one if I blacked the screen, but 6-7 seconds for 64k is quick enough. This should allow a quicker turn around of testing on the C64 version as it downloads under the ROM's and VIC chip, which in turn means I dont HAVE to pack it to run/test it.
Once I've cleaned it all up I'll post the new C64 downloader, along with the wiring diagram - although I suspect its the same as a few others, its very simple: 8 Data wires, 1 signal, and 1 busy - easy. I know loads of folk will simply point out that theres already 1,000,000 downloaders, but from what I saw, they were all far too complicated - I just want download and run!