Motorola 6800 - Move To Austin

Move To Austin

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 transistors 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 provided the control logic for a character base computer terminal. The 6845 had support for a light pen, an alternative to a computer mouse. This was a very popular chip and was even used in the original IBM PC Monochrome Display Adapter with the Intel 8088 16-bit microprocessor in 1981, and in the follow-up IBM Color Graphics Adapter for the original PC and successors; the IBM Enhanced Graphics Adapter card contained custom IBM chips that emulated the Motorola 6845, with minor differences.

The MC6801 was a single chip microcomputer with 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. 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 microprocessor Motorola produced. It had a new instruction set that was similar to the 6800 but abandoned op-code compatibility for improved performance and high-level language support; the two were software compatible in that assemblers could (and generally did) generate code which was equivalent to 6800 opcodes the 6809 did not directly emulate. In that sense, the 6809 was upward compatible with the 6800. The 6809 had many 16-bit operations, including the first 16-bit multiply instruction in a microprocessor, and two 16-bit index registers and stack pointers.