Plus/4 - 121 colors in 1984!

Model:          Commodore Plus/4

Manufactured:   1984

Processor:      7501/8501 ~0.88MHz when the raster beam is on the visible screen and
                ~1.77MHz the rest of the time. (The TED chip generates the processor
                frequency). The resulting speed is equal to the vic-20. A PAL vic-20
                is faster than this NTSC machine, but a PAL Plus/4 is just a little
                faster than a PAL vic-20.

Memory:         64Kb (60671 bytes available in Basic)

Graphics:       TED (7360)
                Hi-Resolution: 320x200
                Colors: 121 (All can be visible at the same time)
                Hardware reverse display of characters
                Hardware blinking
                Hardware cursor
                Smooth scrolling
                Multicolor 160x200
                (No sprites)

Sound:          TED (7360)
                2 voices (two tones or one tone + noise)

"OS"            Basic 3.5

Built in        Tedmon,
software:       "3-plus-1" = word processor,
                spreadsheet, database and graphs.

History and thoughts

The Plus/4 was called 264 as a prototype (January 1984) and was supposed to have customer selectable built in software. But they decided to ship all with the same built in software and rename the computer Plus/4 (June 1984). (The reason for the long delay was that Commodore's factories were busy producing C64s). There was other versions available of the same "TED" computer (more or less): The C16 - Looks like a black Vic20 with white keys but is the same computer as the Plus/4, but with no built in software (except for Tedmon), only 16kb of ram, and no RS232. Why it looks like a vic-20 is because Commodore intended it as a replacement for the vic-20 when it was cancelled in 1984. There was also a C116 with the same features as the C16 but looked like a Plus/4 with rubber keys. About 400,000 Plus/4s were made (compared to 2,5 million vic-20s and something like 15 million C64s).

The reason why the Plus/4 wasn't more popular was one: The C64! Commodore kind of competed with themselves. Let's list the benefits with the two computers:

   * 121 colors (compared to c64's 16)
   * Very powerful basic
   * Built in machine language monitor
   * A little faster
   * Built in software
   * Lower price

   * Sprite graphics
   * Better sound
   * Lots of software available
   * All your frieds have one
   * Your old vic-20 tape recorder will work without an adapter
   * Your old vic-20 joysticks will work without adapters

Well, which would you choose?
Well, Basic 3.5 is quite powerful. It has commands for graphics, sound, disk commands, error handling etc. I counted 111 commands/functions (compared to 70 for the C64). On the c64, POKE and PEEK is the only way to access graphics, sprites and sound. And with most of those registers being two bytes big and the chips a bit complex to set up, that is quite troublesome and time consuming for the basic. And drawing graphics with lines, circles etc using only basic on the c64 is just impossible (or would take a year!) On the other hand - if basic programming doesn't interest you, but copying pirate copied games from your friends, then the c64 is your computer... I mean back then! ;-)

There was more reasons than just the c64 for the Plus/4's lack of success. There are many theories about this on the internet so instead of just repeating them, I would like to contribute with another one: The strange names! Why on earth name the same line of computers so differently! The Plus/4, C16 and C116 is more compatible than a vic-20 with and without memory expansion! And they even look different! I would have made two different computers:

  • "TED-64" (Plus/4) and
  • "TED-16" (The C16, but in a Plus/4 case).

    They would also have normal joystick and tape ports (or adapters included with the computer). The 3-plus-1 software could have been left out and been sold separately on a cartridge to bring down the price of the computer. It could have been sold together with the computer in a bundle at a reduced price if you wanted to. This way the original 264 idea about customer selectable included software could have been doable with all the selectable software on different cartridges.

    My impressions

    I have just got the Plus/4, but my impression of it so far is very positive. It's little and neat. I like the basic and the graphics. The computer has very much "Commodore" feeling. I would say it's like a mix between the vic-20 (for the simplicity, one graphcis/sound chip and default colors), the C64 (for the similar graphics) and the C128 (for the powerful basic and the similarities with the 128's VDC chip features like blinking etc.) The Plus/4 also have the Esc codes that the C128 has. The machine language monitor is also almost the same. But in the same time the Plus/4 is simple and easy to survey like the vic-20. I think it's a well designed computer. The only thing I don't like about the Plus/4 is the lack of a Restore key. But there are work-arounds (Runstop+reset for example). I have written some more tips about this in the manuals below.

    The same people designing the Plus/4 (except for one) later designed the C128.

    If you plan to get a Plus/4, then you might want to know that the 1541 diskdrive is working, the video cable is the same as for the c64 (at least composite and sound that my cable is using). But for joysticks, you need to make a little adapter, also for the tape recorder (if it isn't of the black type that has a built in adapter).

    My Plus/4 is a NTSC machine with a 110V power supply. And living in Sweden I needed to buy a 220->110v converter. The Plus/4 does not need the frequency from the PSU (like the C64), so a simple converter that generates 110v 50Hz is fine. My Plus/4 has a square power plug. Others have a round one, and then I could have used an European c64 power supply instead. There are of course PAL Plus/4s as well, but I got mine for free and I like the NTSC display too. No BIG border around the screen like on all PAL Commodores. The NTSC Plus/4 has also a little faster key repeat, so it feels a little faster even though the PAL version runs faster. BUT - There is MUCH more PAL software available it seems...


    Janne Peršaho and I have made a set of .pdf manuals for the Plus/4, C16 and C116 computers. The package is intended as a sufficient user's manual package (if your computer didn't come with one) as well as a complement to the original manuals.

    Download: (release 7 - released 4 May 2005)

    Includes four documents:

  • basic35.pdf - A detailed Basic 3.5 manual.
  • advanced.pdf - Hardware and advanced basic programming.
  • short35.pdf - A short "ink-saving" basic reminder.
  • tedmon.pdf - A short description of the built in machine language monitor.

    If you have the original manuals, then it's probably enough to print out "advanced" and "short35". However, "basic35" does take up some things left out by the original. Advanced.pdf covers much of the things you wonder about coming from another Commodore 8 bit computer, for example how to make your own character set or if you wonder where the restore key is?

    Here are some complementing documents on other sites:


    My Plus/4 programs

    (Most of them should work on a C16 / C116 as well.)

    Boray Pics

    25 nice pictures for your PAL Plus/4 in three .d64s

    Parasite -
    A little basic demo.

    The Color Table -
    The purpose of this program is to display all available colors and to try out different combinations. It also displays poke codes that can be used in TED registers as well as in the Color/Attribute memory.

    Emulator -
    A toy basic emulator/simulator to simulate the vic-20, c64, c128 and Plus/4.

    Detector -
    A basic routine for detecting which computer your program is running on - for making hardware independent basic programs. Identifies unexpanded and expanded vic-20, c64, plus4/c16, c128 40 column mode, c128 80 column mode and cbm-II.

    Colorful -
    A tiny basic "demo" or test...

    A text formatting and printing program.

    HTML Walker
    Word processing tool / Web file viewer. (Note that you can't use texts saved with the Plus/4's built in word processor without conversion to petascii or ascii.)

    A benchmark program to test the speed of your Commodore 8 bit computer against others.

    textport.prg -
    (May 2004) A program for converting petasc textfiles to ascii. Puts in all the commodore special signs, like {BLU}, {YEL}, {CLR}, {UP}, {SH-W} etc... Useful for publishing program listings. Here is an example: textport.txt (The program's own program listing). The program should work on any CBM 8bit computer with diskdrive.

    Age statistics
    Small statistics program.


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