By 1984 the VIC-20 was old and Commodore needed a cheaper machine to sit below the Commodore 64. Its answer was a new family built around a single chip, the MOS 7360, known as TED. When Commodore first showed the top model it was called the Commodore 264, and the family is still known as the 264 series. Commodore renamed it the Plus/4 when it decided to build four office programs into its ROM, and announced the Commodore 16 at the same time as its cut-down sibling. C16 software runs on the Plus/4, but the C64’s does not run on either without conversion.
Your Commodore reported the British launch in December 1984. The C16 came in a starter pack with a cassette deck, an introduction to BASIC and four recreational programs. The Plus/4 cost £299, with 64K and a word processor, database, spreadsheet and graphics program built in. At full price they had a hard case to make against the C64. The Plus/4 reference guide conceded that “a full library of software is not yet available”, and Your 64‘s reviewer saw nothing to justify the Plus/4 costing more than the 64. Once the price fell, the C16 found a second life: it was £139 in February 1985 and £49.99 in a Your Computer buyers’ guide in June 1986, and by 1988 most of its games came from the budget labels at £1.99.
Fast facts
- Manufacturer: Commodore.
- UK launch: late 1984.
- Models: Commodore 16 (16K, in a case like the VIC-20 and C64); Commodore 116 (the same machine in a smaller case with a “chicklet” keyboard); Plus/4 (64K, built-in software).
- CPU: MOS 7501 or 8501, a 6502-family processor, at 0.89 or 1.76 MHz.
- Video and sound: the 7360 TED; 40×25 text, 320×200 graphics, 121 colours, two tone channels, one of which can play noise.
- Memory free for BASIC: 12,277 bytes on the C16; 60,671 on the Plus/4.
- BASIC: Commodore BASIC 3.5, with commands for graphics, sound and structured loops.
- Price in Britain: C16 £139 (early 1985); Plus/4 £299 (at launch).
One chip for nearly everything
Commodore’s specification describes the TED as a chip “intended for low end 6502 family based personal home computers systems”. It “controls video output … system timing, dynamic RAM control, ROM control, and keyboard scanning”, through 34 control registers, and its hardware features include “Dynamic RAM refresh”, “Sound generation” and “Programmable video time standards”, so the same chip could drive a PAL or an NTSC television. On the C64 the same work is spread across the VIC-II, the SID and two interface chips. The specification’s own summary of the system ends with “Low chip count, high system integration”.
It also set the machine’s limits. The Plus/4 reference guide admits that the machine “does not have sprite graphics, which are available on the Commodore 64, and the Plus/4 music features are not as sophisticated”. The TED’s sound is two square-wave voices, one of which can switch to white noise, where the SID has three voices with envelopes and filters. A game’s moving objects had to be drawn into the character set or the bitmap by the program itself.
A processor that runs faster when the screen is quiet
The TED also makes the processor’s clock, and it changes speed as the picture is drawn. The specification explains that the clock “doubles frequency from 894KHz (NTSC) to 1.788[MHz] (NTSC), during non-display times”. While the TED is fetching characters for the visible screen and refreshing memory, the 7501 runs at the single rate. Outside that window, in the borders and during vertical blanking, it runs at the double rate. Blanking the screen takes this further: “double clock is enabled at all times except refresh”, because the memory still has to be refreshed whether or not anything is on screen.
That is the reverse of the arrangement on the C64 or the Atari 8-bit machines, where the display steals cycles from a processor running at its normal rate. On the TED machines the fast rate is normal, and the display takes it away. Commodore’s service manuals give the PAL machines’ two speeds as 0.89 and 1.76 MHz.
How many colours?
The TED’s palette is a grid of hue and brightness rather than a fixed list: 16 colours at 8 luminance levels. Commodore’s own documents do not agree on the total.
| Document | Figure |
|---|---|
| C16 service manual | “121 Colors (15 colors; 8 luminance levels and Black)” |
| Plus/4 service manual | “128 Colors (16 colors; 8 luminance levels)” |
| Plus/4 Programmer’s Reference Guide | “can produce 121 different colors” |
Both numbers are right. A colour value is built as luminance*16+color-1,
which gives 128 combinations. But one of the sixteen colours is black, and
black at eight luminance levels is still black, so the number of distinct
colours is 15 × 8 + 1 = 121. The Plus/4 service manual counted the encoding;
the other two counted what you can see. Either way it was far more than the 16
colours of the C64. RUN magazine, previewing the machines in November 1984,
managed a third description: “15, each with eight hues”.
BASIC 3.5 and the built-in software
The C16 and Plus/4 share Commodore BASIC 3.5, which added the commands the
C64’s BASIC 2.0 lacked: COLOR, DRAW, CIRCLE, PAINT and CHAR for
graphics, SOUND and VOL for the TED’s voices, and DO ... LOOP for
structured programs. The Plus/4 reference guide puts it plainly: “Graphic
handling is much easier in BASIC Version 3.5 than it is in the Version 2.0
built into the Commodore 64.” A C16 switches on to COMMODORE BASIC V3.5 12277 BYTES FREE.
The Plus/4 added 64K of RAM, of which 60,671 bytes are free for BASIC, a serial port for an RS-232 adapter, and a second 32K of ROM holding the integrated word processor, spreadsheet, database and graphics program. The C116, which a Commodore World quiz of 1997 described as having a “scaled down Plus/4 style case and ‘chicklet’ keyboard”, was the C16 in a smaller box.
The machines also took their own peripherals. The Plus/4 reference guide warns that the machine “is NOT compatible with the DATASSETTE cassette player used with the earlier computers” and needs the new 1531, and that “Older Commodore joysticks are not compatible”. The 1541 disk drive and Commodore’s printers did carry over.
Software was a harder break. RUN told readers in November 1984 that BASIC
programs from the older machines “will load and may run”, but that converting a
C64 program meant replacing its PEEK and POKE commands, machine code might
need its addresses moved, and C64 cartridges were “definitely not compatible”.
The same article listed what the C64 kept: “much richer sound/music”, “sprites
for easy animation” and “faster cassette tape”.
A second life on budget tape
Commodore sold the C16 as the VIC-20’s replacement. Compute! reported in January 1985 that the $100 C16 had taken the VIC’s place. In Britain the price kept falling, from £139 in early 1985 to £49.99 by the middle of 1986.
The budget labels followed. In November 1988 Your Commodore published a C16 and Plus/4 special with a game finder listing every title its writers could track down. They were “pleasantly surprised by the quantity and quality of the C16 and Plus/4 games”, and noted that most were “available through the budget kings such as Mastertronic, Code Masters and Alternative software”. Alternative Software sold all its titles at £1.99, and Elite’s Encore label had reissued Bomb Jack for the C16 at the same price. The guide was meant to “answer critics who claim that there isn’t any C16 or Plus/4 software”.
The machines lasted longest outside Britain. In Hungary, a Budapest shop interviewed by Mikroszámítógép Magazin for its Christmas 1987 buying guide was selling the Plus/4 with a cassette recorder for 18,000 forints and the C16 for 10,000 to 11,000, against 24,000 to 26,000 for a C64, The Plus/4 was still being bought as a family computer after that. In 1989 the magazine reported a family whose Plus/4, bought the year before, now ran a homework system the mother had written in about 300 hours of work, and a programming competition in which a special prize went to Harc az életért (“Fight for Life”), a Plus/4 version of the Game of Life. A magazine devoted to the three machines, C16/C116/Plus4 Computing Monthly, was still appearing at the end of 1989.
Sources
- Your Commodore, December 1984, “Data Statements”: the British launch of the C16 and Plus/4, the starter pack, 121 colours, the Plus/4 at £299.
- Cyndie Merten and Sarah Meyer, Programmer’s Reference Guide for the Commodore Plus/4 (1986): the Commodore 264 renamed the Plus/4, the C16 announced alongside it, 60,671 bytes free, no sprites, BASIC 3.5 compared with BASIC 2.0 (preface, pp. v-vi); 121 colours (p. 186); the colour value formula (p. 205).
- Commodore Business Machines, TED system specification (7501 and 7360), transcribed by Oliver Heun and edited by V. Lidovski (2003): system overview and features (p. 3); the 7360’s functions, registers and features (p. 7); clock doubling and refresh (p. 33); the two voices and noise generator (p. 33).
- Commodore, C16 Service Manual and Plus/4 Service Manual, product specifications: memory, processor speeds, the 121 and 128 colour figures.
- Commodore, Commodore 16 User’s Manual (1984): the start-up message, “COMMODORE BASIC V3.5 12277 BYTES FREE”.
- Your 64, issue 6, February 1985: the C16 “selling at £139”; its cassette recorder and joysticks incompatible with other Commodore machines.
- Your Computer, June 1986: buyers’ guide, “Commodore 16K £49.99”.
- Compute!, issue 56, January 1985, p. 12: the $100 Commodore 16 as the VIC-20’s replacement.
- Your Commodore, C16 and Plus/4 special supplement, November 1988: Bomb Jack in Elite’s Encore range at £1.99; the game finder and the budget labels (p. 31).
- Mikroszámítógép Magazin, 1987 no. 12: Budapest shop prices for the Plus/4, C16 and C64.
- Commodore World, issue 20, July 1997: quiz answer on the C16 and C116 cases.
- C16/C116/Plus4 Computing Monthly, vol. 1 no. 8, November 1989.
- RUN, vol. 1 no. 11, November 1984, p. 34: tables comparing the Plus/4 and C16 with the C64, “Myths about the new computers”, and the colour count.
- Mikroszámítógép Magazin, 1989 no. 6: the family Plus/4 and its homework system; the competition prize for Harc az életért.
- Merten and Meyer, Programmer’s Reference Guide for the Commodore Plus/4: the 1531 Datassette, the 1541 and printers, and the joystick ports.