Fred N. van Kempen <Fred.van.Kempen(a)microwalt.nl> wrote: Well, it's obvious what's happening. The VXT program reads the SID register, sees the top byte equal to 0B, and doesn't know what the heck to do with it. In other words, it just doesn't support this machine. Good. This is what I expected, but just to make sure. The real VT1300 was AFAIK a KA42-A (M30, 90 ns cycle time) with GPX video, so you've just built a better VT1300 with a faster 60 ns cycle time CPU and with SPX video. Given that the VXT program runs on 3 different CPUs (VS2000 with MV II, KA42/VT1300 with CVAX, and VXT2000 with SOC), we can safely assume that your faster VT1300 won't cause any problems later, i.e., the program is very unlikely to time things with CPU cycles. MS