INMC 80 News

While I was disassembling the BASIC I found a number of things that aren’t mentioned in the manual such as ctrl ‘O’. “What is ctrl ‘O’?”, I hear you ask. It suppresses output (long word ‘suppresses’). Can I hear shouts of, “Useless!”? Well its not, because a flag is stored in the workspace. Poke the flag and you suppress output, useful for passwords and the like. Mind you this only works while the BASIC has control of the input buffer. This occurs when the input is in the NAS-SYS or Nasbug X0 mode, or during an INPUT statement.

Ever noticed how slow BASIC is on starting up? Take a look at locations FCCDH through to FCD4H these locations form a routine which is simply a delay. At this point I will grit my teeth and hope that I’m right and that it is all it does.

Ever wondered why you can’t single step BASIC? It’s because it changes the NMI jump vector in the workspace. If you want to single step BASIC ignore any calls to FEBBH because that’s where it changes. Ok so it changes the NMI jump so what does it change it to? It changes it to the break function, so if you can generate an NMI you can use it as a break key. How do I generate an NMI ? Simple connect a push to make switch between pin 4 of the keyboard and ground. (Nascom 2 only. Ed.)

Two little homilies (I’ve just looked that up in the dictionary, it said, “Pedious moralizing discourse.”, I didn’t know how close my choice of words was). Both of these concern the design and/or testing of new equipment, and both are printed here for those just on the point of desparation.

The first came from my father, who spent a lot of my early childhood constructing television sets out of war surplus radar sets. As I remember, they had long persistence green screens. When I first cut my teeth on a soldering iron (and that hurt), he told me, “It will always take so long to build a thing, and then at least five times as long to make it work.”. That one has always stood me in good stead when doubtful homebrew circuits didn’t do as expected. I must admit it’s preserved my sanity, if only in a perverse desire to prove my old man wrong.

The origin of the second is more obsure, I may have even invented it myself. I certainly use it in the shop when customers present themselves with a handful of dud chips. It goes as follows. “One dud is too bad, change it, the second is coincdence, three is ‘Hmmmm’, and four or more, is ‘you’ve done something wrong mate’.” This one proved it’s worth only yesterday, when a customer came in with no less than eight “dud” CD4028s. Now eight is stretching even my credulity a bit far, so after applying the above rule, it turned out that he’d forgotten to connect the power rails to any of the chips. QED.