page_title: Motorola 6800
section_title: Move to Austin
hierarchical_section_title: Motorola 6800 / History / Move to Austin
caption_attribution_description: Motorola M6800 family Peripheral Interface Adapters (PIA). The PIA has two bidirectional 8-bit interface ports each with two control lines. The MC6820 was introduced in 1974 and fabricated with enhancement-mode NMOS. In 1976 the family was moved to a depletion-load technology to reduce chips size and increase speed. The electrical characteristics of the PIA interface were changed and the new part was named the MC6821. The L suffix indicates a ceramic package; the P suffix was for a plastic package.
context_page_description: The 6800 is an 8-bit microprocessor designed and first manufactured by Motorola in 1974. The MC6800 microprocessor was part of the M6800 Microcomputer System that also included serial and parallel interface ICs, RAM, ROM and other support chips. A significant design feature was that the M6800 family of ICs required only a single five-volt power supply at a time when most other microprocessors required three voltages. The M6800 Microcomputer System was announced in March 1974 and was in full production by the end of that year.
  The 6800 has a 16-bit address bus that can directly access 64 KB of memory and an 8-bit bi-directional data bus. It has 72 instructions with seven addressing modes for a total of 197 opcodes. The original MC6800 could have a clock frequency of up to 1 MHz. Later versions had a maximum clock frequency of 2 MHz.
  In addition to the ICs, Motorola also provided a complete assembly language development system. The customer could use the software on a remote timeshare computer or on an in-house minicomputer system. The Motorola EXORciser was a desktop computer built with the M6800 ICs that could be used for prototyping and debugging new designs.
context_section_description: Gary Daniels was designing ICs for electronic wristwatches when Motorola shut down their Timepiece Electronics Unit. Tom Bennett offered him a job in the microprocessor group in November 1974. Bennett did not want to leave the Phoenix area so Gary Daniels managed the microprocessor development in Austin. (Daniels was the microprocessor design manager for the next ten years before he was promoted to a vice president.)
  The first task was to redesign the 6800 MPU to improve the manufacturing yield and to operate at a faster clock. This design used depletion-mode technology and was known internally as the MC6800D. The transistor count went from 4000 to 5000 but the die area was reduced from 29.0 mm² to 16.5 mm². The maximum clock rate for selected parts doubled to 2 MHz. The other chips in the M6800 family were also redesigned to use depletion-mode technology. The Peripheral Interface Adapter had a slight change in the electrical characteristics of the I/O pins so the MC6820 became the MC6821. These new IC were completed in July 1976.
  A new low-cost clock generator chip, the MC6875, was released in 1977. It replaced the $35 MC6870 hybrid IC. The MC6875 came in a 16-pin dip package and could use quartz crystal or a resistor capacitor network.
  Another project was incorporating 128 bytes of RAM and the clock generator on a single 11,000-transistor chip. The MC6802 microprocessor was released in March 1977. The companion MC6846 chip had 2048 byte ROM, an 8-bit bidirectional port and a programmable timer. This was a two-chip microcomputer. The 6802 has an on-chip oscillator that uses an external 4 MHz quartz crystal to produce the two-phase 1 MHz clock. The internal 128 byte RAM could be disabled by grounding a pin and devices with defective RAM were sold as a MC6808.
  A series of peripheral chip were introduced by 1978. The MC6840 programmable counter had three 16-bit binary counters that could be used for frequency measurement, event counting, or interval measurement. The MC6844 Direct Memory Access Controller could transfer data from an I/O controller to RAM without loading down the MC6800 microprocessor. The MC6845 CRT Controller (CRTC) provided the control logic for a character based computer terminal. The 6845 had support for a light pen, an alternative to a computer mouse.
  The MC6845 was a very popular chip: it was even used in the original Monochrome Display Adapter and the original IBM Color Graphics Adapter for the IBM PC and successors, where the 6845 was used with an Intel 8088 CPU.  The later IBM Enhanced Graphics Adapter (EGA) card contained a custom IBM chip (the EGA CRTC) that replaced the Motorola 6845, adding many enhancements, in a mostly-compatible way.  The IBM Video Graphics Array (VGA), which became ubiquitous (to the point that it is still emulated as the baseline functionality of most modern PC video adapter chips) incorporates a compatible near-superset of the EGA CRTC, still mostly-compatible with the MC6845 (but by this point without the light pen support, which the EGA CRTC retained).
  The MC6801 was a single-chip microcomputer (that today would also be called a microcontroller) incorporating a 6802 CPU with 128 bytes of RAM, a 2 KB ROM, a 16-bit timer, 31 programmable parallel I/O lines, and a serial port. (The MC6803 was the same except without the ROM and with fewer different bus configurations.) It could also use the I/O lines as data and address buses to connect to standard M6800 peripherals. The 6801 would execute 6800 code, but it had ten additional instructions, and the execution time of key instructions was reduced. The two 8-bit accumulators could act as a single 16-bit accumulator for double precision addition, subtraction and multiplication. It was initially designed for automotive use, with General Motors as the lead customer. The first application was a trip computer for the 1978 Cadillac Seville. This 35,000 transistor chip was too expensive for wide-scale adoption in automobiles, so a reduced function MC6805 single-chip microcomputer was designed.
  The MC6809 was the most advanced 8-bit m
caption: The M6800 family chips were redesigned to use depletion-mode technology. The MC6820 PIA became the MC6821.
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