nevin1@ihlpf.ATT.COM (00704a-Liber) (02/05/88)
In article <314@upvax.UUCP> aarone@upvax.UUCP (Aaron Nabil Eastlund) writes: .In article <3556@ihlpf.ATT.COM> nevin1@ihlpf.UUCP (00704a-Liber,N.J.) writes: ..Back in the days when I my TI-55 (model I) was working, I was able to get itto ..display the letters ABCD on the display (without turning it upsidedown). Also ..I could make it wait for a key in a program. Does anyone (besides me) know ho ..I did it? . . I remember flogging out the encoding scheme for the TI-55 progs back in Jr. .High, when I was given a TI-55 (state of the art, ya know) to do my trig & .analysis class homework. I believe it was memories 8 and 9 that were used .for "overflow" program storage, somewhere around step 18, and the mapping .between opcode and mantisa/exponent was trivial enough for your basic 14 .year-old (me) to hack out. That's exactly how I did it (I was 14 at the time too--coincedence?? :-)). For those of you who want to try it, store 3.84 in register 9 and run the program. You will get 3D in the display. .Like the 6502, there were more opcodes availiable .than were "documented" (availiable from the keyboard), and some of them .were almost as spectacular as the "halt-and-catch-fire" (6502 again) .op-code. The Z80 also had a few more "undocumented" opcodes. For exampe, instead of treating an index register (either IX or IY) as one sixteen-bit register, you could uses some of the 'extra' opcodes and treat it as two eight-bit registers. .Had you really asserted yourself, you would have found all of the .hex digits, and some other funky functions. I did assert myself. I went through and tried every two-digit code and documented all the functions I found. I wish I knew where I put that sheet of paper! BTW, the only function I was *never* able to duplicate was putting an "F" in the display (that was when I was just storing random numbers in registers 8 & 9). As a side note: the most impressive program I ever saw written for a TI-55 was one that implemented the quadratic formula. My friend (hi Darin :-)) managed to fit it in 32 steps (the entire program memory of the TI-55), although I think he had to 'cheat' a little (either the second root would flash, or you would have to hit '=' after getting the first root). -- _ __ NEVIN J. LIBER ..!ihnp4!ihlpf!nevin1 (312) 510-6194 ' ) ) "The secret compartment of my ring I fill / / _ , __o ____ with an Underdog super-energy pill." / (_</_\/ <__/ / <_ These are solely MY opinions, not AT&T's, blah blah blah