Microprocessor and Microcontroller Based Systems Instructor: Eng.Moayed N. EL Mobaied The Islamic University of Gaza Faculty of Engineering Electrical Engineering Department بسم الله الرحمن الرحيم 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 Pin QD Read/Write Flip-flop latches data bus value onto external pin, when memory location is selected, AND Write is active high whenever port 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 Write Port Write DDR buffer, enabled when pin is output determines whether port bit is input or output 8 of these flip-flops form the "Data Direction" SFR 8 of these the "Data" SFR holds bit output 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 Write Port Write DDR buffer, enabled when pin is output determines whether port bit is input or output 8 of these flip-flops form the "Data Direction" SFR 8 of these the "Data" SFR holds bit output 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 Characteristics The 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, V IH 2.4V(TTL buffer inputs) Maximum Input Low Voltage, V IL 0.8V(TTL buffer inputs) Input Leakage Current, I IL +1  A PIC 16F84A Port Input Characteristics (5V power supply) Digital Input/Output and the 16F84A

Simple Digital Interfacing – connecting to switches 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 V D D V S V D current flows out of the gate and lights led when output is at logic 1 current flows into gate and 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”

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