Andre Adrian, DL1ADR
version: 2026-05-24
The words microprocessor, microcomputer and microcontroller are
related, but describe different kinds of "micro". First, micro is
another word for Large Scale Integration (LSI) computing devices
that appeared in the 1970s. One early example is the "Calculator-on-a-Chip"
Mostek MK6010. This IC contained the CPU, ROM, RAM, IO in one
housing and is a mask-programmed
microcontroller by todays wording. The Zilog Z80 and MOS
Technology 6502 are examples of microprocessors, that is only the
CPU is in the IC, ROM, RAM, IO are external. There was always a
limit of maximum number of transistor functions on a IC. Therefore
"CPU only" microprocessors have more computing power then the
microcontrollers of the same vintage. A microcomputer is the final
product. Be it a game console like Atari 2600, a home computer
like Commodore C64 or a personal computer (PC) like IBM PC.
This web page describes a 8052 microcontroller computer. The Intel 8048 or MCS-48 was first released in 1976. The Magnavox Odyssey 2 game console from 1978 used the 8048 microcontroller instead of a microprocessor. The Intel 8051 or MCS-51 was the more powerful follow-on and first released in 1980. I use the Atmel AT89S52, a microcontroller with Flash memory as ROM. The classic 8048 was mask programmed. The 8748 has EPROM.
The 8052 microcontroller RAM has a small size of 256 bytes. The
8052 allows external program and read/write memory. An external 32
KByte SRAM allows program download thru the build-in UART (serial
port). An UART-to-USB bridge with CP2101 or FT232 completes the
connection to the host computer.
There is discussion about "the first microprocessor" and there is
discussion about "the first microcontroller". The Intel 8080 had
real impact on the market, think of S100 bus and CP/M operating
system, earlier microprocessors had not. The first
microcontrollers had little impact. The german company Olympia
produced the CP-3F, the
german company Nixdorf the NCF1.
Other microcontrollers are SGS-Ates
M380 and General Instruments LP8000. The most prominent of
this bunch was Fairchild F8.
There was a dispute between Olympia (AEG) and Fairchild about "who
stole from whom". Instead of a court battle, both
parties made a license agreement. The Fairchild F8 was, like
the CP-3F and the others, a two chip microcontroller. The second
chip contains the program counter (PC), ROM and IO. The first chip
contains the CPU and "scratchpad" RAM. The Mostek MK3870 combined
both F8 chips into one. There was a mask-programmed version like
the MK3870/42 with 4KByte ROM and 64 Bytes RAM. The MK38P70 was
for development. A "real" EPROM is placed on top of the MK38P70:
The Fairchild F8 was used in one of the first chess computers,
the CompuChess
from 1977. This time, the firmware (ROM program) was stolen by Novag
Chess Champion MK1. See the case Data
Cash Systems v. JS&A. A friend of mine had the Novag MK1
chess computer. It played horrible chess ...
The Fairchild F8 and Mostek MK3870 can not use external ROM or
RAM. The Intel MCS-48 and MCS-51 range of microcontrollers can.
There are ROM-less versions like the 8040 (MCS-48) and the 8032
(MCS-51). The Intel microcontrollers are called "Harvard
architecture", that is separate program and data memory. In
my opinion, there is no "real" Harvard architecture. You can
combine /PSEN and /RD CPU outputs to use external RAM for program
AND data memory.
Ronald Dekker build a tiny
80(C)32 BASIC board. The 8032 is a ROM-less MCS-51 variant.
I use the AT89S52 with 8KByte ROM. I want to port the monZ80
monitor (BIOS) from the Z80
blinkenlights computer to MCS-51 microcontrollers. Then I
want to run MCS BASIC-52 from 1985. This late BASIC has
one-dimensional DIM, 6-bytes BCD floating point numbers and
IF-THEN-ELSE.
The number of ICs or "computer chips" is small. The CPU/ROM/IO
AT89S52, the RAM AS6C62256, a low power 32 KByte SRAM, and two
glue chips 74HC00 and 74HC573. The NAND 74HC00 combines the /PSEN
and /RD output of the CPU to create a "von
Neumann" computer architecture with combined program and
data memory. The octal latch 74HC573 de-multiplexes data-bus and
lower address-bus for the RAM. Last but not least a ready-made PCB
with UART-to-USB bridge is used.
to be continued ...