IAS0430 MICROPROCESSOR SYSTEMS Fall 2018 The 2nd lecture Martin Jaanus U02-308 martin.jaanus@ttu.ee 620 2110, 56 91 31 93 Learning environment : http://isc.ttu.ee Materials : http://isc.ttu.ee/martin
Topics The digital electronics in analogue world Logic functions ( not, nand,nor,xor...) Realization of logic functions (DTL, TTL, KMOP...) Devices with memory (decoders,multiplexers) Devices with memory (triggers,counters)
Digital electronics Digital ( latin language digitis finger, digit) A digital signal is a signal that is being used to represent data as a sequence of discrete values; at any given time it can only take on one of a finite number of valuespõhiline kasutus on kahendsüsteem, sest seda on lihtne kasutada (signaal kas on või ei ole) This contrasts with an analog signal, which represents continuous values; at any given time it represents a real number within a continuous range of values. Usually in digital electronics has also time discrete values.
Binary system Two possible values The simpliest digital system. Bitt. 0 False, missing, low level 1- True, present, high level Fuzzy logic is a form of many-valued logic in which the truth values of variables may be any real number between 0 and 1. It is employed to handle the concept of partial truth, where the truth value may range between completely true and completely false.
The Binary system in elecronics Current based (industrial electronis, automation) 0-4 ma, 1 20 ma, if current is missing, circuit is faulty. In consumer electronics usually voltage based: 0 0...0.5 V, 1 2.4...(3.3 V, 5 V) In industial communication and electronics can be also used other levels 0 >>5 V, 1 < -5V...-24 V (RS232) Logic states can be coded into AC voltage or current -: amplitude,frequency, phase. Modern communication technology. Separation zone
History 1705 Binary system (0,1) Gottfried Wilhelm Leibniz 1886 Georg Boole algebra (logic gates), relay logic 1907 The usage of Audion (electon valve) in NAND gate. 1924 predecessors of modern logic gates. 1941 The first electonically programmable device (Konrad Zuze, Z3), used electronic valves. 1953 The first fully semiconductor based computer. 1958 The first logic IC. Digital control module of automation(1973) USSR
History The usage of simple logic gates has decreased because of usage microprocessors, but anyway those components are hidden inside those devices. The usage of simle logic gates is required when speed is important. Digital control module of automation(1982) USSR
The Binary system in elecronics It is neccecarry that logic gates confirm states, positive feedback is required: The transfer function of inverter.
Logical operation - negation Without this operation the digital electronics is not possible! 0 1 ja 1 0 Y=X X Y X Y
Logical operation negation (inversion) The simpliest way to use one transistor. Transistor must be in closed or saturated state. Discrete components TTL CMOS The CMOS technology is the most popular, it does not consume energy in static state.
Logical operation negation (inversion) The problem in digital circuit transfer to others state must be as quick as possible! Current The solution : Decrease supply voltage (power depends of root of voltage ) and if it is possible working frequency. Cooling Parasitic capacitors need to recharged!
Connecting digital devices The programmer sees only 0 and 1 In real circuit there are existing voltages and currents They are always analogue values! When you design circuits you must take it into account! The next gate consumes energy (CMOS switching, TTL continiously), the output must allow it. In usual case there is possible connect to output 10 next inputs. Low Low High Low High High
Logical operation OR The gate with at least 2 inputs. The output is 1 kui at least one input is 1. Y=X1+X2+...Xn X1 X2 Y X1 X2 Y
Logical operation OR The simpliest realization use diodes. Example from consumer electonics Device is powered from battery OR from power network. Drawback voltage drop in diode is 0.7 V The dicrete elements can used in simpliest application. It is not used inside IC! (1973)
Logical operation AND The gate with at least 2 inputs. The output is 1 if all inputs are 1. Y=X1*X2*...Xn X1 X2 Y X1 X2 Y
Logical operation AND The simpliest realization use diodes.. This operation happens when you connect open collector gates. Data busses (näit I2C) The discrete elements can used in simplest application. It is not used inside IC! Vcc
Combined operations To get all logic funcionality you should have negation (NOT) and one of these AND or OR gate. If you have them, no more is physically required. The basic logic gates are NAND (the most popular) or NOR gates. 1973 The Soviet Union, Texas Instruments 1966
NAND One possible basic logic block The cascade connection of AND and NOT gates. The output is 1 if at least one input is 0 Y=X1*X2*...Xn X1 X2 Y X1 X2 Y You only need this component to make any logic circuit (Charles Sanders Peirce proved in 1880)
NOR One possible basic logic block The cascade connection of OR and NOT gates. The output is 0 if any input is 1 Y=X1+X2+...Xn X1 X2 Y X1 X2 Y You only need this component to make any logic circuit
Exclusive OR (XOR) Two inputs Output is 1 if the inputs are different. Y=X1+ X2 Can be made using NOR or NAND gates. The main usage is inside microprocessor (the part of adder) X1 X1 X2 Y X2 Y http://www.circuitstoday.com/half-adder The half adder
Exclusive NOR (XNOR) Two inputs The output is 1 if inputs are equal. Y=X1+X2 Can be made using NOR or NAND gates.. It can be used in synchronus detector. X1 X2 Y X1 X2 Y The corridor switch
Gates with third state It is not possible to connect outputs of usual logic gates together. It is possible to use gate with open collecor, but then we get additional NAND operation. To make it possible, some gates have possibility to beak the output (move it to high impedance mode high-z) Usually this input is labeled as ENABLE Usage in microprotsessor systems to connect different devices to one bus.
Decoder A binary decoder is a combinational logic circuit that converts binary information from the n coded inputs to a maximum of 2n unique outputs. They are used in a wide variety of applications, including data demultiplexing, seven segment displays, and memory address decoding. http://www.interfacebus.com/ic-bcd-to-7-segment-decoder-schematic.html
Multiplexer A multiplexer (or mux) is a device that selects one of several analog or digital input signals and forwards the selected input into a single line. Transmission line
Multiplekser Has 2 n inputs and n addres inputs Connects selected input with output. The input is detemineb by addres. https://commons.wikimedia.org/wiki/file:mux_from_3_state_buffers.png#/media/file:mux_from_3_state_buffers.png
Demultiplexer (demux) One input, 2 n outputs Connects selected output with input. The output is detemined by addres.
Logic devices with memory (triggers) Can store one bit of information. The information is stored until the power is on. Synchronous trigger ( changes states only during clock pulse) Asynchronous trigger (changes states immediately when input changes) Nonlinearity and positive feedback is required. The idea of memory- hysteresis (1973, USSR)
RS Flip-Flop S - Set, R Reset The simplest memory, but has forbidden state Asynchronous, changes states immediately when input changes. R=S=1 is not allowed!
Synchronisation The logic gates work in real-time (asynchronously). The most of digital systems work synchronously. The states change only when clock signal is active (falling or rising edge of signal or both). CLOCK kell Transition time must be lower than Δt. Clock frequency f=1/ Δt
Synchronous RS flip-flop Reacts only when clock signal is active, usually AND gates are added. State S=1 ja R=1 is forbidden(this is allowed in JK trigger, what is 2 RS triggrs in cascade connection+logic).
D flip-flop (memory cell) D delay > if D=1 then active front of clock switches it always to state 1. if D=0 then active front of clock switches it always to state 0.
The other flip-flops The JK flip-flop augments the behavior of the SR flip-flop (J=Set, K=Reset) by interpreting the J = K = 1 condition as a "flip" or toggle command. If the T input is high, the T flip-flop changes state ("toggles") whenever the clock input is strobed. If the T input is low, the flip-flop holds the previous value. (division by 2) Combined flip-flops. The combination with logic gates. http://www.circuitstoday.com/flip-flop-conversion
Nowdays computer memory RAM Random Access Memory Static (based on flip-flops), thefastest, expencive Dynamic (memory cell capacitor), takes less space, but needs refreshing charge decreases during time. The information is stored until the power is on! SRAM DRAM https://en.wikipedia.org/wiki/random-access_memory
Nowdays computer memory ROM Read Only Memory The infomation is stored even the power is off. The outer connections are similar with RAM. ROM The information is entered in production EPROM information can be programmed by user ( to erase UV light is needed) EEPROM Electrically erasable and programmable memory (slow) Flash EEPROM, same, but faster https://en.wikipedia.org/wiki/flash_memory The drawback of EEPROM memories. There is limited write cycles. The RAM memory can be replaced with flash memory in some cases. The idea of ROM: https://www.cl.cam.ac.uk/teaching/1213/sysonchip/materials/sg3bus/zhp4c6e8640b.html