Denial

It's been nearly 30 years since I bought Jim Butterfield's ML book as a boy, and I've decided to give it another try. This time I'm trying on the VIC-20 for a change of scenery, and I'm wondering if someone can clue me in as to why basic memory seems trashed after running any tiny program (in my case stored in the cassette buffer per the first few chapters of Jim's book) using the VICMON (G)o command? Reading through the VICMON manual I see mention of using the E command to preserve the zero page, but even if I use E 1000 (or E 1800) prior to running my program (then restore with E 0000), upon exiting VICMON and trying to enter a Basic program statement, the machine is trashed and needs to be reset. Can anyone explain to this neophyte why this happens?

Welcome,

This should help

viewtopic.php?f=2&t=7481&p=80550&hilit= ... upt#p80550

If you search the forum there are a few other recent monitor threads.

VICmon does not respect the start-of-BASIC pointer at $2b, and uses it for its own purposes. So when you exit VICmon, BASIC starts at a different location, making it seem like your BASIC program is trashed. It's not really trashed, it's just somewhere else.

You'll need to set the pointer at $2b/$2c back to its proper location every time you exit VICmon. For example, on an unexpanded VIC-20, you'll want to do:
VICmon is terrible in several other ways. I always felt like I was fighting against it. But, this is its most egregious malfunction if you're trying to use it in conjunction with BASIC.

I used to have an EPROM with Vicmon at $6000, Progaid at $7000 and an EPROM with my own utilities at $A000 (with UNNEW amongst others).

To cleanly switch from Vicmon to Basic I did a G FD22, and at the READY., I did a SYS40960 to recover my Basic program.

Regards,

Thanks for the replies, that explains things for me and is very helpful!