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Vic20cr.jpg

History

Origin, marketing

The VIC-20 was intended to be more economical than the PET computer. The VIC-20's video chip, the MOS Technology VIC was a general-purpose color video chip designed by Al Charpentier in 1977 and intended for use in inexpensive display terminals and game consoles, but Commodore couldn't find a market for the chip. With Apple II gaining momentum with the advent of VisiCalc in 1979, Jack Tramiel wanted a product out that would compete in the same segment, to be presented at the January 1980 CES. For this reason Chuck Peddle and Bill Seiler started to design a computer named TOI (The Other Intellect).

The TOI computer failed to materialize, much due to the fact that it required an 80-column character display which in turn required the MOS Technology 6564 chip, which could not be used since it required very expensive static RAM to operate fast enough. In the meantime, freshman engineer Robert Yannes at MOS Technology (then a part of Commodore) had designed a computer in his home dubbed the MicroPET and finished a prototype with some help from Al Charpentier and Charles Winterble. When Jack Tramiel was confronted with this prototype he immediately said he wanted it to be finished and ordered it to be mass produced following a limited demonstration on the CES, since the TOI had not yet been finished.

The very hackish prototype produced by Yannes had very few of the features required for a real computer, so Robert Russell at Commodore headquarters had to coordinate and finish large parts of the design under the codename Vixen. The parts contributed by Russell included a port of the operating system (kernel and BASIC interpreter) taken from John Feagans design for the Commodore PET, a character set with the characteristic PETSCII, an Atari 2600-compatible joystick interface and the cartridge port. The serial IEEE 488-derivative interface was designed by Glen Stark. Some features, like the memory add-in board, were designed by Bill Seiler. At the time, Commodore had an oversupply of 1Kbit×4 SRAM chips, so Tramiel demanded that these be used in the new computer. The end result is arguably closer to the PET or TOI computers than to Yannes prototype, albeit with a 22-column VIC chip instead of the custom chips designed for the more ambitious computers.

In April 1980 at a meeting of general managers outside of London, Jack Tramiel declared that he wanted a lowcost color computer. When most of the GMs argued against it, he said, "the Japanese are coming, so we will become the Japanese." This was in keeping with Tramiel's philosophy which was to make "computers for the masses, not the classes." The concept was championed at the meeting by Michael Tomczyk, newly hired marketing strategist and assistant to the president; Tony Tokai, General Manager of Commodore-Japan, and Kit Spencer, the U.K.'s top marketing executive.

When they returned to California from that meeting, Tomczyk wrote a 30 page memo detailing recommendations for the new computer and presented it to Tramiel. Recommendations included programmable function keys, full size typewriter style keys, built-in RS-232. Tomczyk insisted on "user friendliness" as the prime directive for the new computer and proposed a retail price of $299.95. He recruited a marketing team and a small group of computer enthusiasts, and worked closely with colleagues in the U.K. and Japan to create colorful packaging, user manuals, and the first wave of software programs (mostly games and home applications). Scott Adams was contracted to provide a series of cartridge-based adventure games. Tomczyk's account of the story is told in his 1984 book, The Home Computer Wars.

While the PET was sold through authorized dealers, the VIC-20 primarily sold at retail, especially discount and toy stores, where it could compete more directly with game consoles. It was the first computer to be sold in K-Mart. Commodore took out advertisements featuring actor William Shatner of Star Trek fame as its spokesman, asking, "Why buy just a video game?". Television personality Henry Morgan (best known as a panelist on the TV show What's My Line?) became the ironic voice on a series of clever Commodore product ads.

The VIC-20 had 5K of Ram, which netted down to 3.5K on startup, which is the equivalent to the words and spaces on one sheet of typing paper. The computer was expandable to 32k with an add-on memory cartridge. Although the VIC-20 was criticized in print as being underpowered, the strategy worked: in 1982 it was the best-selling computer of the year, with 800,000 machines sold, and in January 1983 it passed the 1 million unit mark—a first in computer history. At its peak, 9,000 units per day were produced, and a total of 2.5 million units were sold before it was discontinued in January 1985, when Commodore repositioned the C64 as its entry-level computer due to the forthcoming release of the C128 and Amiga (the latter taking Commodore into the 16-bit world).

In 1981, Tomczyk contracted with an outside engineering group to develop a direct-connect modem-on-a-cartridge (the VICModem) which at $99 became the first modem priced under $100. The VICModem was also the first modem to sell over 1 million units. VICModem was packaged with $197.50 worth of free telecomputing services from the Source, CompuServe and Dow Jones. Tomczyk also created an entity called the Commodore Information Network to enable users to exchange information and take some of the pressure from Customer Support inquires, which were straining Commodore's lean organization. In 1982, this network accounted for the largest traffic on CompuServe, which, it can be argued, was an early implementation of Internet-style user groups.

Technical

Hardware Modifications

Improve VIC Video

Vertical Patterns

1. Add a 220 uF Capacitor across the +5V supply to the VIC chip. (You can easily connect between pins 20 + 40 of the VIC Chip).

2. For some reason, there are strong 1Mhz pulses on the Colour output Pin #2. Replacing the simple colour coupling capacitor for a better high pass C-L-C filter (220pf - 10-50microH - 270pf) does the rest. There is room for these components by removing the simple ferrite bead attached to pin 2 (See schematic below)

Colour Phase

1. Red and Cyan. In most cases the colours are clipped due to an incorrectly biased Colour output stage. Placing a 2.7k (estimate, may vary according to machine) resistor from Colour output pin 2 to +5V track pulls the output voltage up and stops the clipping.

2. Blue and Yellow. These subcarrier levels (not phases) are affected by rebiasing the clock chip to the video chip on pin 39. Ferrite beads links can be removed to add the series capacitor or on some models by rebiasing the incoming clock IC on its pin 2 with a pull up 1K resistor and a pot.

Upgrade.gif

Create a new Power Supply

The VIC comes with two different power supplies, depending on the date of manufacture.

Old Style two prong 9V

This is used by the older generation of VIC-20's. The external power supply is a simple 9V transformer, with no electronics included inside it.

This unit is typically very reliable. It is normal for the unit to "buzz" at 60hz lightly.

New Style DIN Brick

This is a similar power supply to the one supplied with the Commodore 64. However, the VIC-20 model has a higher 5V output, so it is not recommended to use a power supply from a C64 on a VIC.

These power supplies are also very susceptible to failure. All electronic components are sealed in epoxy inside the brick and cannot be repaired.

However, it is quite simple to create a new power supply for the VIC utilizing the DIN connector from a failed/suspect supply.

Requirements: 1. 9V AC power supply 1.0A (Some older analog modems have this. It has to be AC for timing signals) 2. 5V DC power supply >2A. These are fairly common, although 2A would require a switching transformer or a rather large wall wart. An old PC power supply will do (the kind with the hard switch).

Din Connector Power2.png

Pin 6+7: Connect to 9V AC

Pin 2: Connect to negative side of 5V

Pin 5: Connect to positive side of 5V

Known ROM Bugs

RS232 DSR + CTS (Hardware Handshaking)

Hardware Handshaking is broken

EFF4  BIT $9120	<--- these should be $9110 not $9120
F512  LDA $9120	

RS232 Read Status

Status Register is lost

FE5D  LDA $0297	Read RS-232 STATUS REGISTER
FE60  LDA #0	     <--- ACC is lost, so we should do
FE62  STA $0297	          LDX #0
FE65  RTS                 STX $0297 

RESTOR Kernel call writes to ROM

RESTOR call falls through to VECTOR. However, this causes STA ($C3),Y to occur, writing to ROM. This can cause trouble with certain hardware.

FD52  LDX #$6D    RESTOR entry point
FD54  LDY #$FD
FD56  CLC      
FD57  STX $C3     VECTOR entry point
FD59  STY $C4
FD5B  LDY #$1F
FD5D  LDA $0314,Y  fix   LDA ($C3),Y
FD60  BCS $FD64    --->  BCC $FD66
FD62  LDA ($C3),Y        LDA $0314,Y
FD64  STA ($C3),Y
FD66  STA $0314,Y
FD69  DEY
FD6A  BPL $FD5D
FD6C  RTS

Peripherals

C2n Datasette

By far, the most common and popular peripheral for the Vic 20 was the C2n Datasette. While disk drives were made available and even specific for the Vic 20, many Vic 20 owners felt that the disk drives were terribly expensive in contrast to the relatively cheap Vic 20 home computer. The Datasette was priced more in line with a Vic 20, generally costing about half of what the computer was new. It provided reliable data storage and retrieval on commonly available audio cassette tapes. While data storage and retrieval was considered slow, a stock Vic 20 computer only had 3.5k available, which meant that the programs written for it were small. As such, for a stock Vic 20 home computer, the performance of the C2n Datasette was acceptable.

C2n.jpg

The Vic 20 was compatible with the same Datasettes used on the Commodore PET computer. This same Datasette was also compatible with the Commodore 64; successor to the Vic 20. Many people who upgraded from the Vic 20 to the Commodore 64 reused their Datasette tape drives. When used with a Commodore 64, which had 38k of free memory which lead to larger programs, the slow speed of the Datasette tape drive became quite apparent, which helped to drive sales of Commodore's 1541 disk drive.

In spite of the popularity of the Datasette drive among Vic 20 computer users, many commercial titles continued to be released in cartridge format in order to avoid the stock Vic 20's 3.5k memory limit. However, with memory expansion, a Vic 20 could load many of these same games from tape.

Memory Expansion

Next to the Datasette, memory expansion was another very popular peripheral upgrade for Vic 20 owners. Many people ran into limits with 3.5k of memory rather quickly; while it was sufficient for simple games and terminal emulators, more sophisticated programs required more memory. Memory expansion was achieved by plugging a RAM cartridge into the Vic 20's cartridge port. With the exception of the 3k expansion solutions, most memory expansion came in 8k blocks and changed the Vic 20's memory map. For memory expansion needs, the 8k RAM cartridge was one of the more popular solutions. 8kram.jpg

VicModem

As the world of computer telecommunications grew with various on-line services and computer bulletin board systems, the VicModem became another popular peripheral for the Vic 20. At the time, it was the cheapest modem available for a home computer. Running at up to 300 baud, one would manually dial the phone number of the service on the telephone, with the cord normally running to the telephone handset plugging into the modem. The modem itself plugged into the user port of the Vic 20, leaving the cartridge port free for telecommunications software cartridges or memory expansion. A red LED on the side of the modem showed you if it was active or not, and a switch on the side would set the modem to "Answer" mode or "Originate" (or call) mode.

Vicmodem.jpg

Protecto-80 Cartridge / DATA-20

This cartridge takes over the video functions of the VIC, and allows the display of 40 or 80 columns B+W, using its own DIN port.

The VIC chip is still functional, so it is possible to setup a dual monitor system. Regular POKE statements can be used to update the original VIC chip screen.

This cartridge has space for expansion memory, which is populated in the Data-20 8K units.

Protecto80.jpg

Memory Map

$9BF0 CAT Controller / data register
$9BFC Mode Register
     Bit 0: Character set. 0 - upper case, 1 - lower case
     Bit 5: 40/80 Columns. 0 - 40 Columns, 1 - 80 Columns
$9FB0-$A7FF - BIOS ROM
$B800 - $BFFF - Video RAM

Programming

Software

Manuals / Documentation

Promotional/Magazine Materials

Byte Magazine, May 1981 VIC-20 Review Media:Bytemay81.pdf

Links

Original Commodore VIC-20 Wikipedia article

Denial Commodore VIC-20 Community