From time to time, I get reader feedback, more information. or notice something I’ve missed mentioning in a previous article. It’s worth collecting such tidbits and presenting them as a group, as I’ll do now.
-SINCUS LIGHT PEN-
(SINCUS NEWS Sep/Oct 1986)
I suggested the possibility of trying a Radio Shack phototransistor in this project, and requested that those trying it tell me how it works. Edward Radtke, of Louisville, KY has tried it, (part # 276-145) and it works fine. Thanks loads, Edward!!
-CAN WE TALK?-
(SINCUS NEWS Nov/Dec 1986) “On Communicating Computers”
I neglected to mention that certain wires in an RS-232 link sometimes need to be swapped, in order to get things working. Some RS-232 ports are configured as Data Communication Equipment, and some as Data Terminal Equipment ( DCE and DTE). The main difference is that the wires at some pins may need to be swapped, so that both devices don’t try to “talk” on the same wire, causing conflict, and “listen” on the same wire, where no one is trying to talk. Since the Async card I use in my PC can be jumped to do either, I was able to use a “straight through” cable. Depending on the particular RS-232 parts you may use, you might instead have to swap the TX DATA and RX DATA lines, and swap CTS and DTR. Be sure to swap the wires at one connector only; if you do it at both, you will “unswap” the fix you just made!!
-TS2068 ROM DISASSEMBLY-
( Started last issue and continuing in this issue )
Starting in this issue, my listing will cover some of the ROM’s uses of the Floating Point Calculator, a “second language” that lies hidden in the ROM. Since the calculator commands are FORTH-like in their use, I’ve used the equivalent words and symbols in the comment column that you would use if you were writing a similiar program in the FORTH language. If you want to learn more about the calculator, there are several sources. If your user group library goes back far enough, you might check some old issues of SYNC ( in it’s second year, I think ) for a series of articles on the floating point calculator in the ZX-81 ( TS-1000 ). These are largely applicable to us. Also, I believe that an article in the short-lived TIMEX-SINCLAIR USER told about it. The article’s title said something about FORTH, but the author spoke mostly about how the Floating Point Calculator works.
[-Ed notes: SYNC, Jul/Aug 1982, “Understanding Floating -Point Arithmetic”, Part 3, page 43, by Dr. Ian S. Logan, 24, Nurses Lane, Skellingthorpe Lincion, LN6 0TT, U.K. -parts 1,2 in earlier issues. ( Other details of the routine in this article can be found in “Sinclair ZX-81 ROM Disassembly, Part B”, Melbourne House, 1982, by Drs. Ian Logan and Frank O’Hara.)
TIMEX-SINCLAIR USER, Vol 1:#4, page 42, “Getting FORTH”, by Bill Payne. Author recommends in addition to above Logan book, also Part A, of the same title. Also “Starting FORTH” by Leo Brodie, Prentice-Hall, 1981 and FORTH Encyclopdeia by Mitch Derick and Linda Baker, Mountain View Press, 1982.]
However, the best source may be found in a 5 part series in ZX-COMPUTING ( a Brtish magazine ). Starting with the July 1986 issue, Toni Baker has been presenting a discourse on the Spectrum calculator, which is directly applicable to us. ZX-COMPUTING will take a VISA or Mastercard number for subscriptions ( so you don’t have to worry about exchanging your dollars for Sterling ).They will also start your subscription with back issues if you request it, so you get the entire series on the calculator. Write them at INFONET LTD, Times House, 179 The Marlowes, Hemel Hempstead, Herts. HP1 1BB, England.