The Sinclair ZX-80 Microcomputer

When I first saw the ZX-80, 1 said, “This is a computer?” It looked far less impressive than most of the hand-held electronic games— it weighed only 12 ounces, and was just slightly larger than pocket-size at 6 1/2 x 8 1/2 x 1 1/2 inches.

The computer comes with a 128-page instruction and BASIC programming manual, cables for loading and saving your programs with a cassette recorder, a “mains adapter” (a 9 V dc power supply) and a switching adapter and cable for connecting the computer to a television set (channel 2).

When I opened the case, I saw the built-in rf modulator. There is no direct video output. The display is 32 characters by 24 lines (black on a white background— a nice touch). The picture on a standard black and white television is only fair, comparable to the OSI Superboard. The inside of the case is sprayed with metallic paint to cut down on rf interference.

The keyboard is the touch-sensitive, plastic overlay type. Most of the keys have triple functions.

The entire computer comprises only a handful of chips. There are, of course, your standard Z-80A, the input and output buffers, 1K of RAM and one ROM chip that includes the character generator, the monitor and a 4K Integer BASIC. Considering the functions that this computer must perform, the Sinclair people have done a good designing and packaging job. I am impressed.

Because the design is so simple, the poor little Z-80A chip has a lot of work to do. This becomes apparent whenever you type in a program. The screen will flicker whenever there is input from the keyboard or output from the computer. Initially this was annoying, but after using the computer I watched for the flicker as an indication that my input was entered correctly.

Back in 1964, when Dartmouth BASIC was only a gleam in the eye of John Kemeny, little did he know that it would still be used 16 years later. Of course, it’s not exactly the same— the ZX-80 doesn’t have matrix instructions or other embellishments. But there are other commands, such as PEEK, POKE, USR, RAND (a pseudo-random number generator) and EDIT (an easy-to-use program editing function), that make this micro a powerful handful.

Most of the commands are entered with a single keystroke by using the shift key. This saves a lot of time when you are trying to type on the tiny little keyboard. (I haven’t been so annoyed with a keyboard since I had to work with the old PETs.)

The selection of BASIC commands is more than sufficient, if you have only 1 or 2K to work with. But, the designers have a trick up their collective sleeve. The commands that are entered with a single keystroke each take up only one byte of memory space. You can squeeze a lot of programming into the available memory.

I have been assured by those who know that you can do machine-language programming by using the PEEK, POKE and USR commands. I didn’t try because I do most of my work with FORTRAN and BASIC. (I start playing Bach fugues in my head when the talk turns to memory locations and hex code.) An experienced machine language programmer, familiar with the Z-80 chip, could have an interesting time with this computer.

Because the BASIC is so simple, the Sinclair people have slipped another goodie into their computer. As you write a program, the computer will examine each line for syntax errors and change the cursor to an S when it finds one. The computer will not accept a line with an error in it. And, when the output of a program is displayed on the screen, you might see an error code, telling you what, if anything, went wrong with your program. (Watch that syntax, or Mama ZX-80 will lay an error code upside your CRT.) These features make writing and debugging a program easy even for a beginner.

The instruction book that comes with the ZX-80 is first-rate. The instructions assume that you are a rank beginner and take you from the initial power-up of the computer all the way to writing your own programs. Individual chapters explain the function of various commands and the logic behind them. There are many sample programs for you to enter and run. The instructions encourage you to experiment with the programs.

A colleague remarked that if you wanted to learn BASIC, it would be cheaper to buy the ZX-80 than it would to take a college course. Not only would you have access to the computer whenever you wanted it, but you could keep it or sell it when you finished.

The Sinclair ZX-80 lists for $199.95. (I’ve also seen advertisements for the MicroAce computer, which bears a striking resemblance to the ZX-80, for $149.00 in kit form.) Sinclair plans to release an 8K floating-point BASIC and a 16K memory expansion (the ZX-80 has an expansion connector at the rear of the case). There is also a new publication devoted to the ZX-80 called Syntax ZX80.

Conclusions

The ZX-80 is a real computer and an excellent value, but only if you are new to microcomputers or an experienced programmer. The beginner can take full advantage of the instruction manual and only an experienced Z-80 programmer can get the most from so simple a microcomputer.