microprocessor and microcontroller based systems
DESCRIPTION
بسم الله الرحمن الرحيم. The Islamic University of Gaza Faculty of Engineering Electrical Engineering Department. Microprocessor and Microcontroller Based Systems. EELE 4315 — Fall 2010. Instructor: Eng.Moayed N. EL Mobaied. Lecture 9. - PowerPoint PPT PresentationTRANSCRIPT
Microprocessor and Microcontroller Based Systems
Instructor: Eng.Moayed N. EL Mobaied
The Islamic University of GazaFaculty of EngineeringElectrical Engineering Department
الرحمن الله بسمالرحيم
EELE 4315 — Fall 2010
Lecture 9
Almost any embedded system needs to transfer digital data between its CPU and the outside world. This transfer falls into a number of categories, which can be summarised as:
Direct user interface, including switches, keypads, light emitting diodes (leds) and displays;
Input measurement information, from external sensors, possibly being acquired through an analog to digital converter;
Output control information, for example to motors or other actuators;
Bulk data transfer to or from other systems or sub-systems, moving in serial or parallel form, for example sending serial data to an external memory.
How can we provide the required interface between the microcontroller core and the outside world? More precisely, how do we get the data onto or off the data bus at the right moment?
Why Digital Input/Output?
Digital Input/Output and the 16F84A
Parallel Output
We could apply a circuit like this for output.
Here a pulse on the Port Select line captures data on the bus at that instant, and transfers it to the external pin.
Data Bus
External Pin
Port Select
QD
Two lines of
External PinQD
Read/Write
Flip-flop latches data bus value onto
external pin, when memory location
is selected, AND Write is activehigh wheneverport address is selected
Digital Input/Output and the 16F84A
Parallel Input
Data Bus
External Pin
Port Select
Two lines of
buffer transfers logic value on external pin
onto data bus line, when memory location
is selected, AND Read is active
External Pin
Read/Write
Or we could apply a circuit like this for input.
Here a pulse on the Port Select line transfers data on the external pin at that instant to the data bus.
Digital Input/Output and the 16F84A
A Bi-Directional Port Pin Driver Circuit
Or, we could combine both circuits into one multi-function circuit, like this. You don’t need to grasp all the detail of this circuit, although it’s neat if you can.
There is now an extra flip-flop, labelled “Direction”. The state of this decides in which direction data will flow.
The two flip-flops shown can each form one bit in an SFR, which can be controlled from the CPU.
A group of these bits, each driven by a circuit like this, is called a “port
D Q
D Q
"Direction"
"Data" I/O Pin
Read/Write
Port Select
Direction Select
Data Bus
(bit n of an 8-bit port)
(bit n)
Output Buffer
Input Buffer
Alternate Input Function
"Data" SFR
"Direction" SFR
Read Port
WritePort
WriteDDR
buffer, enabledwhen pin is output
determines whether portbit is input or output
8 of these flip-flops form the "Data Direction" SFR
8 of these
the "Data" SFR
holds bitoutput value
flip-flops form
D Q
D Q
"Direction"
"Data" I/O Pin
Read/Write
Port Select
Direction Select
Data Bus
(bit n of an 8-bit port)
(bit n)
Output Buffer
Input Buffer
Alternate Input Function
"Data" SFR
"Direction" SFR
Read Port
WritePort
WriteDDR
buffer, enabledwhen pin is output
determines whether portbit is input or output
8 of these flip-flops form the "Data Direction" SFR
8 of these
the "Data" SFR
holds bitoutput value
-flip-flops form
Digital Input/Output and the 16F84A
Holds output data
Value held determines data direction
Output buffer
0 on this line enables output buffer
From Option Register
Decoded address lines
Digital Input/Output and the 16F84A
Port Input Characteristics
When designing with microcontroller digital I/O one needs to have an understanding of their electrical characteristics.
16F84A Input CharacteristicsThe input of a logic gate or port pin requires the voltage to be below a certain maximum in order to be recognised as a logic 0, or above a certain minimum to be recognised as a logic 1.
Minimum Input High Voltage, VIH 2.4V (TTL buffer inputs)Maximum Input Low Voltage, VIL 0.8V (TTL buffer inputs)Input Leakage Current, IIL +1A
PIC 16F84A Port Input Characteristics (5V power supply)
Digital Input/Output and the 16F84A
Simple Digital Interfacing – connecting to switches
Vi
VS
RVi
VS
R
Vi
VS
Digital Input/Output and the 16F84A
Light Emitting Diodes (leds) - Review
High Efficiency Red Yellow
Digital Input/Output and the 16F84A
a) Gate Output Sourcing b) Gate Output Sinking Current to LED Current from LED
Driving LEDs from Logic Gates (and hence Port Bit Outputs)
I
R
D
I
R
VD
D
VS
VD
current flows out of the gateand lights led when output is at logic 1
current flows into gateand lights led when output is at logic 0
Digital Input/Output and the 16F84A
PIC Microcontrollers Families
PIC controllers are roughly classified by Microchip into three groups: baseline, mid-range, and high performance.
Within each of the groups the PICs are classified based on the first two digits of the PIC’s family type.
However, the sub classification is not very strict, since there is some overlap.
For this reason we find PICs with 16X designations that belong to the baseline family and others that belong to the mid-range group.
Baseline PIC Family
This group includes members of the PIC10, PIC12, and PIC16 families.
The devices in the Baseline group have 12-bit program words and are supplied in 6- to 28-pin packages.
The microcontrollers in the baseline group are described as being suited for battery-operated applications since they have low power requirements.
The typical member of the Baseline group has a low pin count, flash program memory, and low power requirements.
Baseline PIC Family “PIC 10 Devices”
Baseline PIC Family “PIC 12 Devices”
Baseline PIC Family “PIC 12 Devices”
Mid-range PIC Family
The mid-range PIC family includes members of the PIC12 and PIC16 groups.
According to Microchip, the mid-range PICs all have 14-bit program words with either flash or OTP program memory.
Those with flash program memory have EEPROM data memory and support interrupts.
Some members of the mid-range group have USB, I2C, and converters A/D.
Mid-range PIC Family
Implementations range from 8 to 64 pins.
This is by far the most extensive PIC family.
Currently, over 80 versions of the PIC16 are listed in production by Microchip.
The Microchip website has more detailed information on these devices.
Mid-range PIC Family
High-Performance PIC Family
The high-performance PICs belong to the PIC18 group.
They have 16-bit program words, flash program memory, a linear memory space of up to two Mbytes, and protocol-based communications facilities.
They all support internal and external interrupts and have a much larger instruction set than members of the baseline and mid-range families.
High-Performance PIC Family
The PIC18 family is also a large one, with over 70 different variations currently in production.
The PIC18 family uses 16-bit program words and are furnished in 18 to 80 pin packages.
Microchip describes the PICs in this family as high-performance with integrated A/D converters.
They have 32-level stacks and support interrupts.
The instruction set is much larger and starts at 79 instructions.
The PICs in this family have flash program memory, a linear memory space of up to 2 Mbytes, 8-by-8 bit hardware multiplier, and communications peripherals and protocols.
High-Performance PIC Family