Commodore 128

The Commodore 128 (also known as the C128, CBM 128 or the C=128) was the last commercially released 8-bit home computer released by Commodore Business Machines (CBM). Appearing in 1985, three years after its predecessor, the bestselling C64, the C128 was significantly expanded, featuring a redesigned case, a keyboard with a numeric keypad, 128 kB of RAM (externally expandable to 640 kB) and an 80-column RGB monitor output (driven by the 8563 VDC chip with 16 kB dedicated video RAM).

The C128 also featured two CPUs: the primary CPU (the 8502) could run at a maximum 2 MHz clock rate, whilst the secondary processor consisted of a Zilog Z80 that was used for for mode-selection of the computer upon boot-up and ensuring CP/M compatibility. However, the machine was not a multiprocessing system as the two processors could not run concurrently.

The Commodore 128 had three modes of operation: C128 Mode (native mode), CP/M Mode and C64 Mode. The native C128 mode ran at 1 or 2 MHz with the primary CPU and had both 40- and 80-column text modes available, whilst the CP/M mode used the secondary CPU in either 40- or 80-column text mode. The C64 mode was almost 100% compatible with the earlier Commodore 64 computer and allowed users to play C64 cartridges and programs. The Z80 chip was essential for all these modes as it controlled the bus on initial boot-up and checked to see if there was a CP/M boot disk, if there were any C64 or C128 cartridges present, and if the Commodore key (C64-mode selector) was active on boot-up. Based on what it found, the chip then switched to the appropriate mode of operation.

The machine had three disk drives (the 1570, 1571 and 3.5 inch 1581), which gave faster transfer speeds and allowed for more complex drive data arrangements; a feature not available to PC users. The disk drives also had more on-board RAM than the C64, and a far higher proportion was available for BASIC programming, which made it possible for BASIC program code to be stored separately from variables. This greatly enhanced the C128's ability to handle complex programs.

In 1986, an updated version of the system was released: the Commodore 128D, which featured a detached keyboard and a 1571 disk drive in the same box as the main system unit. This provided a more stylish, professional looking unit, much like that of a desktop PC.

Although the C128 sold a total number of 4 million units between 1985 and 1989, it had limited popularity compared to that of its predecessor, the C64. The unit was discontinued in 1989.

Specifications

CPUs

• MOS Technology 8502 at 1 or 2 MHz
• Zilog Z80 at 4 MHz (effectively running at 2 MHz due to stopping half the time to allow VIC-II video chip access to system bus)

RAM

• 128 kiB system RAM
• 2 kiB 4-bit dedicated colour RAM (for the VIC-II E)
• 16 kiB or 64 kiB dedicated video RAM (for the VDC)
• up to 512 kiB REU expansion RAM

ROM

• 72 kiB (28 kiB BASIC 7.0, 4 kiB MLM, 8 kiB C128 KERNAL, 4 kiB screen editor, 4 kiB Z80 BIOS, ca. 9 kiB C64 BASIC 2.0, ca. 7 kiB C64 KERNAL, 4 kiB C64 character generator, 4 kiB C128 character generator) - expandable by 32 kiB Internal Function ROM (optional; for placement in motherboard socket)

Video

• MOS 8564/8566 VIC-II E (NTSC/PAL) for 40-column composite video (a TV set can be used instead of a monitor if desired)
  • Direct register access through memory-mapped I/O
  • Text mode: 40x25, 16 colours
  • Graphics modes: 160x200, 320x200
  • 8 hardware sprites
  • 2 kiB dedicated 4-bit colour RAM, otherwise uses main memory as video RAM
• MOS 8563 VDC (or, in C128DCR, the 8568) for 80-column digital RGBI component video, compatible with IBM PC CGA monitors, monochrome display also possible on composite video monitors; usable with TV sets only when the set has SCART and/or baseband video-in sockets in addition to the antenna connector.)
  • Indirect register access (address register, data register in mapped memory)
  • Text mode: 80x25, 16 colours (not the same as those of the VIC-II)
  • Graphics modes: 640x200, 640x400 (interlaced)
  • No hardware sprites
  • 16 kiB dedicated video RAM (64 kiB standard in 128D, 128 was upgradable to 64 kiB), accessible to the CPU only in a doubly indirect method (address register, data register on VDC, which in turn are addressed through address register, data register in mapped memory)
  • limited blitter functionality alleviates this RAM bottleneck

Sound

• MOS 8580 SID synthesizer chip
  • 3 voices, ADSR controllable
  • White noise channel
  • Cost-reduced and noise-reduced version of C64's MOS 6581; some early C128s have 6581s

I/O Ports

• 8-pin DIN plug containing composite video output, separate Y/C outputs, and sound input/output
• Integrated RF modulator antenna output via a RCA connector
• 2 x screwless DE9M game controller ports (compatible with Atari 2600 controllers), each supporting five digital inputs and two analog inputs.
• Cartridge expansion slot
• PET-type Datassette 300 baud tape interface
• User port (edge connector with TTL-level RS-232 signals, for modems, etc; and byte-parallel signals which can be used to drive third-party parallel printers, among other things; with 17 logic signals, 7 GND and voltage pins, including 9 V AC voltage)
• Serial bus (serial version of IEEE-488, 6-pin DIN plug) for CBM printers and disk drives
• RGBI video output (DB9-connector, identical to IBM PC CGA connector, but with an added monochrome composite signal)