Today we are used to luxury of fully integrated microcontrollers - all key components are conveniently integrated into single reliable part: non-volatile memory, SRAM, CPU core, PLL, ADC/DAC, PWM, serial ports, e.t.c It was not like that in the past and embedded systems typically required lots of chips, until Intel 8048 (MCS-48) was released in 1976 on n-MOS technology. Intel expected that 8048 will have limited product lifetime, and in 4 years, in 1980 it was replaced by 8051 (MCS-51) which conquered the world. It was first high-volume product to integrate 4KiB of PROM, 128 bytes of SRAM, GPIO, serial port as well as 8-bit core in a single crystal. 87C51FC variant was using 32KiB EPROM non-volatile memory instead of PROM's, double SRAM size (256 byte), C-version was manufactured on CMOS process - which makes it exceptionally modern for the time. It was not particularly fast - simplest commands took 12 clock cycles to execute, so even at 20Mhz it was doing just over 1 million operations per second, also - no 16-bit division commands. Modern 8051-compatible cores are much faster and often do single-cycle command execution.

Recently I got my hands on D87C51FC-20, and decided to experience the old ways of embedded software.