Posted By
Gaia on 2012-01-25 15:09:44
| ACIARe: First Beta Release of Diag264 (0.2B)
@siz: this is amazing, I wouldn't have thought that there was a significant difference other than the ACIA. I mean I may have known earlier about the lack of a PIO in the C16 but totally forgotten by now. So we have one more way to detect the machine type. I wonder how the C116 looks since that was probably the earliest spinoff of the 264 line and the C16 the last one.
@crock: well, there is not much use really, other than perhaps testing. There are no interrupts, no keyboard, no DMA, only single clock and 5 RAM refresh cycles per line. Now as I write this I realize that even with the TED turned off you would get different results due to the RAM refresh. The 8 bit counter is incremented by one on each access and the area $FFxx is read. So that's what makes reading open address space look totally random (though it's predictable). Read here:
http://plus4world.powweb.com/ma.php?maid=154&h=ram%20refresh
And here is some more black magic on bus accesses: http://plus4world.powweb.com/ma.php?maid=23
EDIT: well, from here it appears that the C116 had the 74LS125, too: link
|