|This is the most important chapter in the book. It tells you how to connect up and switch on your ZX-80.
The ZX-80 consists of two units:
(1) The computer
(2) The power supply
The power supply used should be 9 volts DC @ 600 mA unregulated, terminated with a 3.5 mm jack plug. The tip of the jack plug must be positive.
DON’T PLUG IN TO THE MAINS SUPPLY YET
Look at the back of the ZX-80 computer. You will see four sockets. Three of these are 3.5 mm jack sockets marked MIC, EAR and POWER. The fourth is a phono socket for the video cable.
The connection diagram shows how to connect up the ZX-80 to the power supply and to a domestic television which will be used to display the output for the ZX-80.
A video cable with a coaxial plug at each end is provided to connect the TV to the computer.
A twin cable with 3.5 mm jack plugs at both ends is provided to connect the ZX-80 to a cassette recorder. Don't worry about this for the moment.
Connect the power supply to the ZX-80 by plugging the 3.5 mm jack plug into the socket marked 9V DC IN (if you do get it in the wrong jack socket you won't damage your ZX-80 even if you switch on the power. It won't work until you get the plug in the right socket, though!)
SEE DIAGRAM BELOW
Connect the TV using the coax lead provided. You will have to tune the TV to the ZX-80 frequency approximately channel 36 on UHF, so check that you can do this — most TV sets either have a continuously variable tuning control or, if they select channels with push- buttons, have separate tuning controls for each channel. If your set is a push-button set select an unused channel (ITV 2, perhaps). Turn down the volume control. OK — we can't put off the moment of truth any longer! Switch on the TV.
When it has warmed up ... SWITCH ON THE ZX-80.
Connecting up the ZX80
You will be disappointed to see a horrible grey mess on the screen!!
Try tuning in the TV set. At some position of the tuning control the screen will suddenly clear. At the bottom left hand corner of the screen you will see a curious symbol — a black square with a white letter K in it.
If you can't see the K, turn the brightness control up until you can see it; you may find that adjusting the contrast control improves legibility. You may be planning to use your ZX-80 a lot. If so it may be worth considering buying a second-hand black-and-white TV to use with the ZX-80. They can be bought cheaply - in the UK, at least.
STORING PROGRAMS ON TAPE
Before you can store programs on tape you'll have to write a program. The rest of this book is all about writing programs, so the first thing to do is to read on until you've got a program to store...
...and now that you have we can start.
The twin coax cable with 3.5 mm jack plugs is used to connect the tape recorder to the ZX-80. Most cassette recorders have 3.5 mm jack sockets for MICROPHONE and EARPIECE. If you have one of those, just connect the 3.5 mm jack plugs as shown in the diagram. On other recorders DIN sockets are used. DIN plug to 3.5 mm jack plug connecting leads are available from most Hi-Fi shops. Consult the handbook to find out how to connect up the plug or plugs.
Once you have done this, connect up the cassette recorder to the ZX-80. Set the tone control (if any) to MAXIMUM. Some recorders have separate TREBLE and BASS control. In this case set TREBLE to MAXIMUM, BASS to MINIMUM. set the volume control to about 1/2 or 3/4 of MAXIMUM.
Have you got that program?
Unplug the MIC plug or DIN plug from the recorder and use the recorder's microphone to record the program's title; if you haven't recorded your voice saying the program's title, you will have trouble in finding programs when you've got a lot of them on tape. Stop the recorder. Reconnect the plug to the recorder. Get into command mode. Start recording and then type SAVE (E key) and NEWLINE.
The screen will go grey for about 5 seconds, then you'll see a series of horizontal streaks across the screen. After a few seconds the screen will clear and will show the program listing.
You will want to check that the program has been SAVED. Unplug the EAR plug. Rewind the tape until you get back to your voice. Now play back. You will hear your title, then you may (or may not) hear a short buzz followed by about 5 seconds of silence. You will then hear a peculiar sound, rather like a supercharged bumble bee. This is the program being played back via the loudspeaker. After a while the sound will change to a loud buzz. Rewind until you are at the beginning of the 5 second silence. Reconnect the EAR plug. Start playing back and then type LOAD (W key) NEWLINE. The screen will go grey or black and after a few seconds it may start looking grey but agitated. After a few more seconds the screen should clear to show a listing of the program.
Note: when you SAVE a program you also SAVE all the data and variables. You can avoid deleting these (RUN clears them) by using the command GO TO 1.
If it doesn't, use BREAK (SHIFT SPACE) to stop LOADING. If this doesn't work, unplug the power from the ZX-80 for a few seconds. Try repeating the procedure using different volume control settings. If this doesn't work, are you using the cassette recorder on mains power? Try again using battery power. If this fails, check the wiring to MIC and EAR.