A micro controller unit (MCU) is an integrated circuit consists of processor core
(CPU), memory (RAM and ROM), and programmable input/output peripherals
(I/O). It is designed for control an embedded system. An MCU can be viewed as
a single-chip computer used in an embedded system.
A microprocessor unit (MPU) has surrounding chips that support various functions
like memory, interfaces, and I/O. The main differences between MCU and
MPU is MPU typically run on an operating system that allows multiple processes
to run at the same time and use Drivers to support peripherals.
4.9.1 MCU processing speed
4-bit MCU, The micro controller can process 4 digits binary code at a time. It is
used on some single device remote. It is cheaper than 8-bit MCU and widely on
low end electronic product.
8-bit MCU, The micro controller can process 8 digits binary code at a time and
it is widely used in multi device and universal remote application.
16-bit MCU, Seldom use in remote application
32-bit MCU, Seldom use in remote application
4.9.2 MCU type
Flash ROM
? It can also termed as Flash EEPROM and it is faster than normal EEPROM.
? Flash ROM is a non-volatile storage technology (memory that can retain the
stored information even when not powered) that can be electrically erased
and reprogrammed.
? Flash IC can be programmed for many times.
OTP ROM
? One Time PROM, IC can only be program once and can’t be reprogram.
? It is cheaper than Flash IC.
Masked ROM
? The program is hard-code by “IC mask” for Silicon wafer fabrication.
? Then the wafer is cut into required IC dimensions for IC package.
? The program cannot be change after the IC masking.
? It always need a masking tool charge and also a MOQ on IC wafer production.
? Normally it comes in die form for cost consideration, so Iit is better for volume
production at the lowest cost.
Other features (MCU with internal oscillator)
? It needs fewer external components.
? They can provide more I/O pins.
? Can keep high frequencies inside IC.
MCU with low operating voltage at 0.9-1.5V, can power by using single dry cell,
such as AA x 1pc at 1.5V.
4.9.3 Memory type
MCU has 2 sections of memory, ROM and RAM, and it also can connect to external
memory IC.
ROM Read Only Memory)
? for storing the program in the MCU.
RAM (Random Access Memory)
? temporary (Volatile) storage area in the MCU for program to run and storing
temporary data.
EEPROM (Electrically Erasable Programmable Read-only memory)
? An be an external non-volatile memory to MCU for storing data that need to
be retained even not powered.
? It is ranged from 2K bit up to 512K bit for use in storing required remote code
library.
Flash Memory
? It is also an external non-volatile memory to MCU for storing data.
? The two main types of flash memory, NOR flash and NAND flash.
? It offers larger memory size than EEPROM.
? The large block sizes used in flash memory erasing has significant speed advantage
over EEPROM when writing large amounts of data.
4.9.4 MCU Programming
Microcontrollers originally programmed only in assembly language, and later it
commonly uses high-level programming languages, such as C++, Python and
JavaScript, for microcontroller in embedded systems. Compilers and assemblers
are used to convert both high-level and assembly language codes into a
compact machine code for storage in the micro-controller’s memory.
Depending on the MCU type, the program memory can be permanent masked
in IC fabrication, programming at the factory for read-only memory, or it can be
an alterable flash or erasable read-only memory.
MCU masking
? The compiled program is sent to MCU IC manufacturer and it is then transformed
into a part of IC circuitry for photo-etch onto the IC body.
? It is hard-coded on the IC and the program cannot be changed afterward.
? It needs an initial masking charge.
There are 2 kinds of MCU Programming in factory:
Offline programming
? MCU is programming before soldering onto the PCB.
? It uses an IC programmer and a suitable IC package adaptor for programming.
? It can be IC program one per time, or several IC program at the same time.
Online programming
? MCU is firstly soldering on the PCBA.
? PCB has connector or contact pads for connection to IC programmer.
? Connection wire length and production environment interference must be
considered.
? If an error is found during testing, the failed PCBA can be re-burned without
disassembling the MCU.
IC Package Type
IC Fabrication
? Raw material Silicon (SiO2) is going through various processes to form the IC
base material wafer in circular shape with thickness about 0.5mm and diameter
ranges from 100mm (4 in) to 300mm (12 in).
? It then uses Photolithography, a kind of Ultra Violet light radiation, to imprint
the IC circuitry pattern on the surface of the silicon wafer.
? It then undergoes doping process to customize and alter the electrical properties
of silicon to create a layer of P or N regions.
? After that, there is Metallization process for deposition of conductive materials
to provide the critical interconnection paths between the separate devices
on the chip. It also provides bonding pads to its exterior package.
? At last is the Etching process for removal of the silicon dioxide layer from
selected regions across the wafer and the photo-resist was removed after
development.
? After the wafer testing, it is wafer dicing process that use a fine diamond cutter
to separate the wafer into individual IC, it is the die form IC and going
through electrical testing to assure the IC performance.
? The separated chips (die) are then bond to the package substrate by use Aluminum
wire. It is then use molded plastic cap to form the final IC shape and
perform the final testing.
IC Package
Die IC
? Numbers of IC is fabricated in a circular wafer form and then cut to required
IC dimensions. This cut out single chip is called a die.
? It gives the lowest cost of IC for product manufacturing use.
? Die IC need use Aluminum or Copper wire bonding process for connection to
PCB
? After IC bonded, it need covered with a black epoxy, normally oval shape, for
protection purpose.
Package IC
? The die IC is wire bonded to a standard package form depends on number of
wires and application.
? There are over 50 types IC package available and normally for remote are
SSOP, SOP, TSOP for small size IC and QFP for medium size IC.