Digital Systems II: Intro Beginnings J. Schmalzel R. Polikar

Digital Foundations §The basic model of a computer system: CPUMEM I/O

Central Processing Unit (CPU) §Controls §Executes §Computes (Fixed- and/or Floating- Point)

Memory §Program store §Data storage §High-speed  Low-speed §Volatile, Non-volatile l RAM, ROM, FLASH (EEPROM) §Fast  Slow

Input/Output (I/O) §Communication between CPU and outside world §Fast  Slow §Standardized (e.g., IEEE b) §Parallel (IEEE 1184)  Serial (USB 2.0)

Hierarchical View of EP and Digital Systems CPUMEM I/O Gates Boolean Algebra Design Techniques MSI Functions State Machines Interface Method Computer Architecture Operating System HLLs

Sequential Circuits  Include feedback  Presence of a clock  Behavior is no longer simply a function of the inputs--must be evaluated synchronously with clock  Flip-flops l D-type l J-K type l etc.

CK QD D-F/F Excitation Function: Dn = Q n+1 Q* P C P C D n Q n X X X 1 0 Illegal 0

Xilinx F/F’s FDC: D-F/F w/ asynchronous clear FDS: D-F/F w/ synchronous set The FDS will not set upon activation of the set input without also activating clock

State Machines  Mealy: Outputs depend on states and on inputs.  Moore: Outputs depend only on states.  One-Hot: A type of Moore machine in which there is one F/F per state.

State Machine Models (& One-Hot) Inputs State Memory Combinatorial Network Clk Moore Outputs Mealy Outputs

Sequential Circuit Design  Problem statement  State diagram  Transition table  Simplified excitation functions  Implementation  Verification

Example Design a sequence detector that will identify SM 1011 Z

State Diagram Input Input/Output Name Output Name MooreMealy

One-Hot SMs §Moore machines are glitchless since outputs change only synchronously with clock. §For relatively small numbers of states, techniques of F/F minimization are largely counterproductive with available “sea-of- gates” FPGA. l A 12-state SM: Don’t bother to reduce/encode. l A 16-bit counter: Definitely encode states.

SM for 1011 Sequence Detector Reset Found1 Found2 Found3 Found4 Z Found None Note: Dashed lines show non-resetting algorithm.

Transition Table Output Present StateInputNext State Z F0 F1 F2 F3 F4 X F0’ F1’ F2’ F3’ F4’

Excitation Functions The Transition Table could be large: 2 6 = 64, but since this is a One-Hot SM, there can be only one state active at a time. When writing the BA for each excitation function, listing the complemented states is redundant. For example: DF0 = F0X* + F2X*, instead of DF0 = F0F1*F2*F3*F4*X* + F0*F1*F2F3*F4* X* Similarly, DF1 = F0X + F1X + F4X DF2 = F1X* + F3X* + F4X* DF3 = F2X DF4 = F3X

Simplification §If there are any redundant terms, can simplify; however, for One-Hot approach, there are no simplifications possible since must account for every separate state path.

Implementation Assign one D-F/F per state and complete the combinatorial network required for each input. Implementation of F0 is shown: Clk & & + DQ F0 F2 X* The final network output, Z = F4. For reset, use asynchronous F/F inputs: Preset F0 and clear F1-F4. P

Verification §Check that the SM performs as required. §More complex input vectors are required since the internal state memory expands total possible states. §Use simulation tools.

The Power of One-Hot Design §Can skip transition table--“read” the implementation directly off the state diagram: Found1 1 1 Found None Clk & & + DQ F1 F0 F1 X X C

Sequential Circuit Functions  Counters  Binary, BCD  Ripple, Synchronous  Registers and Latches  PIPO, PISO, SIPO, SISO

In-Class Lab  Refer to EP Schematic  What is the function of U5?  Explain how it operates--what is the address of LED3?  How does it drive the LEDs?  What currents are supplied (in or out) by the 74HC259 to light up the LEDs?

In-Class Lab  What is the function of U5? Addressable latch to control annunciators.  Explain how it operates--what is the address of LED3? An I/O write to address (CS1+2) enables the D-F/F, Q2.  How does it drive the LEDs? A logic 1 output forward- biases the LEDs, turning them on. The current-limiting resistors prevent excessive forward current. Assuming Vf of the LED is approx. 1.7 V, the current through the diode would be about ( )V/470  = 5.5 mA (which is nearly one of the specified load currents!). When an output is a logic 0, the associated LED is zero biased, which won’t turn it on.  What currents are supplied (in or out) by the 74HC259 to light up the LEDs?

Digital v. Analog Electronics  Digital: Concerned with (usually) only two logic levels. Uses saturating logic circuits. For example, “1” = 5.0, “0” = 0.0  Analog: Concerned with potentially infinite number of values between two extremes. For example, 0.0 < V < 5.0.

In-Class Lab  ESD Principles  Brief tour of Z-World Core Module  Assembly notes  Software notes  Demo

ESD Principles §Minimize electrostatic charge generation §Neutralize charges §Drain off charges §Minimize electrostatic fields and discharge effects §Protect ESD-sensitive devices during handling and transport Treat every device as if it were ESD sensitive!

Electrical Model of ESD Field Equipment Probe Snap (Wrist)Snap (Mat) 1 M 

Assembly Notes §Objective is to add headers and other components to add test points and features. §Good construction practices. §Good soldering practices.

Introduction to Embedded Processors §Into the model of an embedded computer system: CPUMEM I/O

Introduction to Embedded Processors: User v. Developer §User l Transparent product/performance l Low-cost l Excellent interaction design §Developer l Meet schedule and budget (Reuse earlier S/W and H/W--finish project w/o forgoing sleep) l Meet marketing’s specifications l Do it better than the last time

Digital Foundations: The Architecture of an EP §The basic model of a computer system: CPUMEM I/O

The Bus-Oriented EP CPUMEMI/O Add Data Con

Bus Basics Need to provide a shared medium that prevents contention. Use of these methods provides a way to provide bidirectional signal paths. Of course, does require arbitration. Tri-State: “1” “0” and “High-Z” Open-Collector (Drain): Passively pulled high (“1”) or actively pulled low (“0”) AY E A E Y X 0 Z

Example EP Feature List §Small footprint §25.8 MHz CPU §40 CMOS-compatible parallel I/O lines §Four CMOS-compatible serial ports; max async rate of 806 kbps, max sync rate of 6.45 Mbps §8-bit data bus §13 address lines §Control signals (I/O read, write) §Master/slave config §Reset input, output §5, 8-bit and 2, 10-bit timers §256K flash EPROM, 512KB SRAM §RTC §Status, WDT outputs

Questions, Comments, Discussion