Dear Editor

The ZX80’s black-on-white video output is somewhat hard to read. Most computers have a black background with white letters. There is a simple way to reverse the ZX80 video output.

The video input to the RF modulator comes from an exclusive OR gate. One input to this gate is the sync signal and the other is the data. The data input comes from pin 7 of IC9, a 74LS165. This is the Q̄ output of the parallel to serial converter. On the bottom side of the PC board near IC9 are 3 points marked A, B, and C. A goes to the exclusive OR gate, B to the Q output (pin 9) of IC9, and C goes to the Q̄ (inverted) output (pin 7). Presently A is connected to C. To reverse the output, break the connection between A and C and make a new one between A and B. Or you could install a switch to switch between the 2 different outputs.

Thanks for your magazine. It should be a big help to all ZX80 owners in the future.

Brent Dix, Cedar City, UT

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Here is a TAB subroutine listing. It causes the display to tab to any column, 1-32 left to right. Just give COLTAB a value corresponding to the desired column number and insert a subroutine call in your program.

 900 GO TO 2000
 999 REM TAB
1000 IF COLTAB>32 THEN RETURN
1005 LET ITAB=PEEK(16420)-(34-COLTAB)
1010 IF PEEK(16420)<2 THEN LET ITAB=33-(34-COLTAB)
1015 IF ITAB<1 THEN RETURN
1020 LET JTAB=1
1030 PRINT " " ;
1040 IF JTAB=ITAB THEN RETURN
1050 LET JTAB=JTAB+1
1055 GO TO 1030
1060 REM AS CONTINUING PART OF
1061 REM "PRINT ;" "GO SUB 1000"
1062 REM CAUSES TAB TO COLUMN
1063 REM IN "COLTAB" (1-32,
1064 REM LEFT TO RIGHT)
1065 REM "COLTAB NOT CLEARED.
1066 REM "COLTAB" MUST ALLOW
1067 REM SPACE FOR ALL
1068 REM INFORMATION PRINTED.
2000 STOP

(Listing appears exactly as on a TV screen. In line 1005, COLTAB is one word, as is ITAB in line 1010.–AZ)

To add another tab setting, add a ; to the end of your first print command, then assign another value to COLTAB. Insert another GO SUB and PRINT statement and the display will print in two columns.

William Herron, San Diego, CA

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I have an engineering background but am a raw beginner when it comes to computers. Could you put me in touch with other San Diego area ZX80 owners so that I could contact them to exchange ideas and questions?

H.S. Wake, San Diego, CA
[phone number omitted]

To respect your privacy, we will not print subscriber names and numbers, unless you request that your name or number appear.–AZ)

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Congratulations on the first issue of SYNTAX ZX80. My ZX80 programs just fit in memory, but there is not enough left to handle variables or display. Machine language programs run faster and use less memory, but I don’t grasp the essentials of this method. How about an article or series on machine language? I look forward to future issues of SYNTAX.

Mark Paulkus, New Britain, CT

Coming up.–AZ