Archive for March, 2023

Entex MAC

March 4, 2023

In this blog I try to talk only about computers with the understanding that computers are devices a user can execute programs on that haven’t been contained on this computer before (I am aware that this definition of a computer helps only to distinguish between, let’s say, dedicated word processors and computers in our sense. Using this definition, an Amstrad PCW is a computer, a Magnavox VideoWriter is not).

But there are some devices that stretch that definition, I must admit. One of these devices is the very cool, but barely-a-computer Entex M.A.C. that I want to explore in this post.

Entex Industries was an US-American toy and electronic game manufacturer that existed from 1970 to the early 1980s. Their toy lineup included a Lego-like system called Loc Blocks and model kits. As its high times it wasn’t a too small company either with sales exceeding $100 million in 1980. The “Entex” company name derived from NTX, which were the initials of two of the company’s founders. The company logo was an Royal Air Force bullseye with a smiling face overlayed on it.

The electronic games Entex produced (mainly handheld and tabletop electronic games, often mimicking arcade games) were adressed at the more high-end market. The three highlight products for me from these products are the Bike Computer (not a game, but indeed a computer for your bike if you don’t mind to have a medium sized tabletop calculator sized thing on your bike handle), the Adventure Vision tabletop console (exceedingly rare, especially in working condition), and the “Multi-functional Advanced Computer” or MAC Mini Computer (and no, Apple could not sue them, Entex had this name much earlier and was probably bust anyway by the time the Macintosh came around).

The package promises “The First Fun Home Computer for Kids and Adults with Game, Music, Math and Programming Capability”. It reveals a slick, red plastic device with a calculator-like keyboard, a display with a 4×4 (full-size) LED matrix, and a (VFD) 8-digital numeric display beyond. The right side of the case contains a series of small black cards with holes and some description on it.

But before we dive into the software aspects, let’s look at what makes this device interesting to me: the use of 2 4-bit chips of the family of the world’s first microcontrollers: The Texas Instruments 1000 series. This series of 4-bit chips were first used in 1972, being beaten by Intel’s 4004 CPU chips by only a short time (the 4004s were no microcontrollers, but required quite a number of chips for a complete system). The 1000 series was first used in TI’s own calculators before they were sold to everyone from 1974 on. The 1000 series contained ROM, RAM, counters, timers, and I/O interfaces and was used in a plethora of toys and calculators.

The 1000 series models Entex used in the MAC was one TMS 1600 with 4000 bytes of ROM, and 64 bytes of RAM (yes, bytes, not kilobytes), and a TMS 1170 with 2000 bytes of ROM, and another 64 bytes of RAM, and the interface to run a VFD display (therefore, the 1600 in the MAC dealt with making music and the programming, and the 1170 did the calculator and the games). The ROMs are mask-programmed, this means that the ROM content is added during manufacturing of the chips and cannot be changed later on. This makes for smaller production cost, but also maximum inflexibility, because if you want to change the software in the ROMS, you have to produce new controller chips. For good measure the two microcontrollers are complemented by a TMS 1024 “Interface Expander” that deals with addressing the 4×4 LED matrix.

Let’s now look at what the MAC came with and what it could do.

The Manual

Normally, we do not talk much about manuals because they either state the obvious or are, in the best case, boring but useful references. For a toy, the expectations are normally even lower.

However, this isn’t a suspicious leaflet by an Asian manufacturer translated by the half-blind daughter of someone who used other Asians manuals to learn English, but a very decent 50-page (at least in German) brochure by a knowledgeable expert in the field, probably the engineer who designed the entire device. Therefore, the MAC manual surprises with accurate, detailed information, giving the big picture of how computers change the world (at the time), and concrete assistance for the user. This is partly really needed because there is so much non-obvious functionality, and partly it is way more information the user really needs because he/she cannot use it anyway.

The “punch cards”

As I wrote above, the MAC comes with a series of black cards that ressemble a little bit computer punch cards, and one asks oneself how the MAC reads these holes. The disappointing answer is, it doesn’t. The cards can be inserted in a slot on the top of the display in order to hide some of the LEDs for some applications. If you play the Tic-Tac-Toe game for example, it reduces the 4×4 matrix to the 3×3 one needed for the game and for some applications it also adds some inscriptions to the LEDs so you know which button to press to address this LED position.

The Calculator Mode

The calculator is a very basic run-of-the-mill 4 species calculator with one memory slot and 8 digits (my machine displays 00000000 when the number overflows, this seems strange to me). Together with the VFD display and the calculator keyboard, this functionality feels very much like the spritual home of the hardware. 10 of the 50 pages of the manual explain the calculator using many examples.

The “Music” Mode (a.k.a Beep Machine)

You have two modes for making music (or noise): piano and organ. The tone does not differ in both modes, the only difference is that in organ mode the tone is held as long as you press a key. You can either play “live” or record and play back songs. You have two octaves of tones, but you can play only monophonically. In record mode you can also access the half tones. In this mode you can even vary the length of tones and add pauses of different length. I don’t know much about music, but what I know is that the tones are played VERY LOUDLY.

The Games and Applications

There are 5 games and applications contained in the MAC. There is a 2-player Tic-Tac-Toe game where (inexplicably) the users have to decide themselves whether someone won the game, a game called Tactics that I do not really understand, a game called Concentration that I do not really understand, a tool that can calculate the local time in a number of cities given an entered time and time zone code, and finally some sort of slot machine (which I do not really understand). All in all, nothing exciting.

Programming Mode

The other thing that really interested me was the programming mode. You can have up to 55 commands and the P1 key starts a program and halts it (and then you can re-start it again by P1). When a program reaches the end, it simply starts over again. I was really baffled though when I learned the commands. You have commands to play tones, to switch on the LEDs for an amount of time, and to switch off all lights. That’s it. That’s not exciting at all. Err, wait, and then there is an example program in the manual that gives you a digital die. How can you program a random die with only these commands??

This is the place where you could try to figure it out yourself. I have given you all the information you need to know. It took me a while to understand it.

Ready? Ok, the randomness comes from the user, i.e. the point in the program execution when he or she presses P1. The program consists simply of the sequence of all numbers on the die that are displayed on the LEDs one after another, and the one that you roll is the one that is currently displayed when you press P1. As the computer runs through the program so fast you can neither distinguish the numbers on the LED matrix nor react fast enough, you cannot control which number the program stops in. Genius!

Of course the lack of any flow control commands means that all your programs have to fit into this scheme or they are programs that need to be always the same. You have a metronome program as an example and you can play melodies or have pretty patterns using the LEDs.


Some of the Entex electronic products were also available under different names in some countries. The MAC was also sold under the name “Multifunktions-Spiel-Computer” by the giant German mailorder company “Quelle” (their main catalog was over a 1000 pages and was printed in 8 million copies). This Quelle version might have been sold the most because nowadays this is the version that seems to be available more often.

I have the Quelle version, which means a (sometimes not very knowledgable) translated German manual and German cards (and because the German card descriptions would need more space, most of the cards instead just refer to the corresponding manual page).

The battery compartment of my MAC is so mucky that I did not want to clean it. Therefore, I can report that the MAC runs just fine on a 6V universal power supply with a 2.5mm plug (plus on the outside, minus on the inside). The MAC package says the device needs 250 mA.

When opening the MAC and looking at the PCB (and you need to unscrew basically everything for that, undoing some 15 screws, including two tiny ones holding the on/off siwtch), I found that two of the TI chips have Japanese-style markings on them indicating that maybe at least the PCB was soldered in Japan (see Photo).

Also, as expected by the use of the microcontrollers, there is not much else going on on the PCB component-wise, some resistors and capacitors, a few transistors, the three chips, the LCD, the VFD, and that’s it. This is, of course, very appropriate for a toy.


The Entex MAC is an early toy computer with interesting hardware and an attractive esthetics. It has an unexpectedly good manual, but is limited in its capabilities due to the restrictions of what could be delivered at the time in a toy. It cost $80 in 1981 at a time when e.g. a 16kB 8080A-based Interact “R” home computer was advertised for $249 (because the remaining inventory of the closed original manufacturer was sold off).

From a collector’s point of view the Entex MAC is a relatively rare thing, but maybe not many people want to have one because it falls a little bit in the void between a game and a computer.

Technical Data

1 TMS 1600 N2LL Microcontroller
1 TMS 1170 NLHL Microcontroller
1 TMS 1024 NLL Input/Output Expander
with together 6000 Bytes Masked-Programmed ROM
and 128 Bytes RAM
4×4 red LEDs
8-digit VFD numeric display
27-key keyboard
Uses 4 C batteries or a 6V, 250 mA power supply with a 2.5 mm plug, plus on the inside
Initial price: $80 ($260 in today’s money)