A minimal system containing a 3850 and 3851 also included four 8-bit data ports, 64 bytes of RAM, and a user program on ROM.

More important, Mostek re-arranged the assembly line so user code in ROM was added at the last step, greatly reducing the cost of customizing the design for controller use.

Best known as a manufacturer of typewriters, Olympia also had a long history in mechanical calculators, a market that was rapidly converting to electronic versions.

Shortly after returning to the US, Chung quit GI and moved to Fairchild where he became lead designer of the F8,[1] and is named as the primary inventor on the patent.

As the case dragged on, in February 1976 Fairchild announced a cross-licensing deal with Olympia for the F8, meaning they now had legal access to the original CP3F design and GI's lawsuit was neutered, at least in technical details.

In contrast, designs like the 8080 and 6800 required separate dedicated-purpose ICs to provide these functions, normally seven,[5] so an F8 system could be implemented for far less total cost.

[1] Although the F8 was marketed as a general-purpose microprocessor, historically it represents the first purpose-designed 8-bit microcontroller,[a] a design that implements a complete computer system on a small number of ICs.

Its release had a profound influence on the market, and led to the introduction of dedicated microcontrollers from most other vendors, among them the Intel MCS-48, Motorola MC6801 and MOS 6510, all of which combined various systems formerly left to the circuit board designer to implement.

Whereas the 3859 was essentially just a single-chip 3850/3851, the 3870 was a significant advance; it ran up to 4 MHz, double that of the 3859, and required only a single +5 V power supply instead of +5 and +12.

A much more important change was that custom ROM code was now masked onto the IC as the very last step in the process, so all of the CPUs were identical until the end of the production line.

Among the most important of these was the addition of a socket on top of the chip that allowed an EPROM to be plugged in with no other support circuitry required.

Mostek merged with United Technologies in 1979, who drove the company into the ground and in turn, sold it to Thomson Semiconducteurs in 1985.

A typical computer system generally requires a CPU, some form of input/output to communicate with the outside world, and memory holding the program code and user data.

Depending on the design, the I/O would communicate with the processor over a dedicated bus, or alternately by placing data in memory and then having the CPU read it.

Other designs sometimes multiplexed the address and data lines so the same pins could be used for multiple functions, at the cost of requiring more cycles to complete an operation.

[10] This freed up 11 pins that would otherwise be used for additional address lines, which, along with other simplifications and splitting of duty, allowed the CPU to have two complete I/O busses.

[10] With only 1 KB of ROM and 64 bytes of RAM, only small programs can be managed, but for many systems, like cash registers, gasoline pumps and similar roles, this is more than enough.

[11] These interface with the PSU and contain additional logic for handling their associated memory; for instance, the 3852 had a complete address bus able to access 64 KB of RAM and the circuitry needed to refresh the data.

The PSU is still required in these systems, and the program counter and other pointers are maintained separately in all of these chips by reading the same control lines.

The main difference between the 3852 and 3853 was that the former included the dynamic RAM refresh circuitry and a 3-pin link to the 3854 DMA controller, while the 3853 removed these and added a new interrupt handler and timer.

It maintained its own address register and a separate byte count, which together indicated the block of memory to be read or written.

PC1 was referred to as a stack pointer but was not actually used for this, it was used only to store the return addresses from subroutines and lacked any push or pop instructions.

For instance, the Load Register (LR) instruction came in 14 different versions depending on the origin and destination of the data.