Document Sample
ECU Powered By Docstoc
					Memories and Silicon Chips

               How The ECU Works.


A digital microprocessor is an array of tiny switches and circuits,
each of which has the ability to do a few simple things. From this
extremely simple basic decision making ability comes all the
functionality of modern computers. Arithmetic and logical
operations can be synthesized to solve a problem, like setting the
pulse widths of an injector.
               How The ECU Works.


Microcomputers use Quartz crystals that resonate at a particular
frequency to coordinate internal operations. Some microcomputers
with very fast crystals and circuitry perform millions or even
billions of instructions per second. Using amplification circuitry,
a digital microcomputer has the capability to activate or deactivate
external circuits , for example controlling the earth path on a fuel
               Memories and Silicon Chips


Just like human memory, electronic memory is simply any device
that stores information for future use. This information is
stored in an electronic memory as a collection of binary digits
(or bits). Memory is therefore a feature of digital systems and not
of analogue systems. This information is usually stored in digital
memory groups of 8 bit words (bytes), or 16 bit words.
Microcomputers, calculators and an increasing number of
digital systems make extensive use of memory.
               Memories and Silicon Chips

Diagram to show the basic
microcomputer system

       Input                               Output
       (keyboard)                          (VDU)

               Memories and Silicon Chips


The previous diagram shows the way in which the memory is used.
Here data flows between the memory devices a central processor
unit (CPU) and between input and output devices. In a computer
system such as this, memory is categorized either as random access
memory (RAM) or as read only memory (ROM). Both types of
memory may be made from thousands of transistors form as an
integrated circuit on a small chip of silicon.
In addition to RAM and ROM semiconductor storage memories,
data may be stored outside the system on tape, disk or C.D.
          Memories and Silicon Chips
RAM type of memory is extremely fast, and can be written to
and read from. Data in RAM is lost when electric power is
switched off, unless a battery back up is provided, so another
means are required to store data while the ECU is turned off.
Computers use RAM as a scratch pad to store data used or
generated by a computer program, as well as instructions
themselves which tell the computer how to manipulate data i.e.
a program or software.
A simple program might fetch a few data values (numbers), add
them, output a signal of a certain duration and then start
repeating over again - which is the basic function of the fuel
injection ECU.
          Memories and Silicon Chips
Programmable Read Only Memory (PROM) retains it’s data
when power is switched off, but it can only be read from, not
written to. PROM is ideal for storing programs and data that
never change. PROM’s are written or “blown” in a special
machine that uses UV light as the writing medium and may
contain numbers that represent commands (data). The ECU
transfers this data (instructions) to the RAM on start up.
          Memories and Silicon Chips
Electrically Erasable PROM (EEPROM) is slow and cannot hold
much data, but it can be read and written to and retains data
when power is off. EEPROM’s are ideal if data needs to be
changed if the vehicle is modified i.e.. a cam change will alter
volumetric efficiency specifications.
          Memories and Silicon Chips
The arithmetic logic unit (ALU) of a computer performs all
mathematical and logical operations based on instructions from a
program and generates codes that notify the program as to
whether they were successful. The ALU performs it’s operation
using it’s own high speed memory.
The ALU is part of the CPU which controls ECU operations
and is usually located in a microprocessor or silicon chip.
          Memories and Silicon Chips
The input/output (I/O) system controls the movement of data
between the computer and the outside devices with which it
communicates (actuators/sensors etc).

Analog to digital circuitry onboard the microprocessor converts
analog voltages into digital numbers that are meaningful to the
ECU and useful in computations.

The CPU/RAM/ROM/I/O are all connected together using a
data address BUS which enforces a strict protocol defining when
a device on the bus may move data to another device so that the
bus can be shared by all.
           Displays, Encoders and Decoders
Decoders and Encoders

In digital electronics, decoders and encoders are important output and input
functions of a system. They are code translators, (they change information
from one form to another).

• A decoder is used to alter the format of information taken from a system.

• An encoder is used to alter the format of information entered into a system.
               IN              OUT      IN            OUT

 Encoder                                                          Decoder

                    SYSTEM                   SYSTEM
       Displays, Encoders and Decoders
Decoders and Encoders

An example of a decoder is a BCD to seven segment decoder/driver. This
device is required to change the 4 bit code produced by a BCD counter into
signals capable of displaying decimal numbers on a seven segment display.
An example of an encoder is a telephone keypad which converts a telephone
number into a string of binary digits for transmission along a telephone line.
Decoders and encoders are examples of combinational logic devices and it
is quite possible to construct them from AND, XOR etc. logic gates. However
purpose designed integrated circuit packages are available to make the job
easier for the circuit designer.
       Displays, Encoders and Decoders
Decoders and Encoders

For example, decoders are used in seven segment displays for converting 4 bit
BCD codes into patterns of 1s and 0s for operating the LEDs in seven
segment displays. These decoders are known as seven segment decoders/drivers.
They are called decoder/drivers since they decode from binary to decimal
and provide the necessary current to light (drive) the LEDs in the display.

                            The 7447 decoder/driver.
       Displays, Encoders and Decoders
Decoders and Encoders

The seven segments of a seven segment LED display are labeled a-g. In the
range of TTL devices (transistor-transistor logic), the 7447 is a device/decoder
designed to drive the segments on or off to display the decimal numbers 0 to 9.
The diagram shows the connections required between the 7447 decoder/
driver and the segments of a common anode display. The output terminals
of the 7447 are connected to the corresponding cathode terminals of the
segment LEDs. Note that in this common anode display all the anodes of the
segment LEDs are connected together to +5v. This means that the outputs
a to g of the 7447 have to go LOW (0 volts), to light the corresponding
segments and produce a number. The use of current is low, around 40mA per
       Displays, Encoders and Decoders
Decoders and Encoders

The CMOS (complimentary metal oxide semiconductor) equivalent of the 7447
decoder/driver is the 4511 device. The outputs of this decoder/driver are active
HIGH so it has to be used with a common cathode display. Each output of
the 4511 sources up to 5mA of current when operated from 10V power supply.
The 4511 decodes the ten 4 bit binary numbers, 000 to 1001 and produces
the following patterns of 0s and 1s for driving the seven segments of a common
cathode display. Note that the 4511 does not activate segment d when showing
decimal 9, or segment a when showing decimal 6, as is normal in digital
watches, clocks and calculators.
          Displays, Encoders and Decoders
    Decoders and Encoders - CMOS 4511
BCD inputs           Segment outputs                    Number

D     C    B    A     a    b    c       d   e   f   g

0     0    0    0    1     1    1       1   1   1   0   0
0     0    0    1    0     1    1       0   0   0   0   1
0     0    1    0    1     1    0       1   1   0   1   2
0     0    1    1    1     1    1       1   0   0   1   3
0     1    0    0    0     1    1       0   0   1   1   4
0     1    0    1    1     0    1       1   0   1   1   5
0     1    1    0    0     0    1       1   1   1   1   6
0     1    1    1    1     1    1       0   0   0   0   7
1     0    0    0    1     1    1       1   1   1   1   8
1     0    0    1    1     1    1       0   0   1   1   9
         Displays, Encoders and Decoders
 Decoders and Encoders

When the LT test input is 0, all the
segments are turned ON. When the BI is         LT = light test
0 and the LT is 1 all the segment are blanked. BI = binary input
                                               EL = enable

Shared By: