I’ve noticed an interesting feature on my 4K ROM: when I enter PRINT USR(623) (NL), I get a clear screen with a solid cursor in the lower left-hand corner. Then if I try to enter lines of program text, I get a “bar code” effect displayed instead of alphanumeric symbols.
The Z80 machine language routine that I actually run loads the I (interrupt) vector register with the value in the accumulator. Using my own value instead of that in the accumulator, I obtain other strange values and characters on the screen. These routines have no effect on actual programming, but seem to change only the video pattern on the TV screen.
David Shulman, Peabody, MA
For those who want to program with this bar code generator, only NEW (NL) wipes it out. When I printed numerals 0 through 9, I got logical bar sequences that could probably be easily read by the ZX80 or an outside device.–SB
With a tape recorder and 1K RAM, I have flawless recording and play-back with both ear and mic cables attached at all times. With the 16K RAM attached, however, a hum develops about halfway into the 5-second silence, ruining the tape for further LOADing.
Robert Keller, Rochester, MN
We’ve had the same trouble, but not steadily. First of all, make sure you’ve hooked up the right power supply. Next, use a pencil eraser to clean the connector’s finger contacts–grime can cause humming. On our 8K machines, the 16K RAM appears to overburden its own power supply as well as the standard one, so we hooked up power through a transformer and adjust voltage back to 9V whenever it dips.–SB
Is there a way of modifying the ZX80 so that the cursor could traverse a line when holding the key down? Is there a loading effect problem if one wants to bypass the RF modulator (Ch. 34) for direct video for a monitor?
R. Allan Smith, Sunland, CA
For direct video, try a high-impedance monitor. A 50-75Ω monitor needs an emitter-follower as described in Sinclair’s technical manual. As for cursor movement, Softsync’s games use continuous cursor movement, but we haven’t read the code yet.–SB
Responding to an INPUT statement with EDIT isn’t fatal! About all that happens is that the screen has been cleared and the current line written into the edit buffer. Just use the cursor and RUBOUT keys to wipe out the copy of the current line and type in valid input. If the INPUT statement was for a string, you must, of course, put in the quotes–but at least you don’t have to pull the plug.
Jim Williams, Calumet City, IL
I’ve had interference problems with the TV display since purchase of my ZX80. The ZX80 is connected to a 12-inch black-and-white TV, but I’ve had no success with the fine-tune adjustment. I also tried removing nearby metal objects.
Richard Nunley, Moline, IL
Try playing with the horizontal hold. The contrast-brightness combination also makes a big difference, and this varies from set to set. Your problem may be RF interference–see Herb Sturges‘ hint on page 9. Herb also noticed poor soldering in his video cable had melted plastic insulation separating the signal carrier and ground. Take a look.–SB