ELEC 4601 Microprocessor systems Lab 3 Tutorial Interrupts

Objectives • Interrupt controller • Timer • Display controller

Interrupts 1) Understand Interrupts and their use in a microprocessor-based system • “An interrupt results in the transfer of control to a new program location. ” a. What is the sequence of operations that occur during an interrupt? b. What are the signals that appear on the bus during an interrupt cycle? c. What is the Interrupt Vector Table and how is it used?

Interrupt Controller (8259 A) 2) Understand the Programmable Interrupt Controller (8259 A) and it’s interface to the 8086 on the SDK Board • What are the key signals that connect the 8259 A to the 8086? • What is the Interrupt Mask Register and how is it used? • How are interrupt priorities handled using the 8259 A? • ICW 1, ICW 2, ICW 4, OCW 1, OCW 2.

Timer (8253) 3) Understand the Programmable Interval Timer (8253) • What is the function of 8253, and how is it used? • How is the 8253 connected to the 8086 and the 8259 A (review Appendix B) • How are the counters initialized and loaded? • What signals are used to clock the counters? • Do all counters use the same clock?

Simplified Block Diagram CLK 0 Counter 1 PCLK 2. 45 MHz Counter 0 CLK 1 IR 0 IR 1 IR 2 ? ? ? ? H Counter 2 Timer 8253 ? ? H CLK 2 PIC 8259 • Counter 0 holds 5 FB 4 H = 24, 500 d. What is the period for CLK 0? – 10 ms • What is the data needed in counter 1 to get CLK 1 period of 1 s? – 10, 000 d = 2710 H Further study: Appendix B

Parallel Port (8255 A) and Keyboard Display Controller (8279) 4) Understand the Parallel Ports chip (8255 A) – How can the 8255 A be used to interface the 8086 to a D/A Converter (review Lab 2) 5) Understand the Keyboard Display Controller (8279) – How do you write to display RAM using the 8279? – How can you address the 7 -segment LEDs on the SDK-86?

Seven Segment Display Table • What you need to display “ 0”? – a, b, c, d, e, f – Hex: 3 F • What you need to display “ 1”? h – b, c – Hex: 06 • LED_TABLE Bits h g f e d c b a DB 3 FH ; 0 DB 06 H ; 1 . . . How can you use it? - LDS, XLAT

Reading Materials for Prelab From your class notes: • Communication Between I/O and CPU (pages 122 -124) From the Peripherals Handbook: • Read about the 8253, 8255, 8259, and 8279 From the 8086 Hardware Reference Manual: • Read the section on interrupts. • Look up information for the LDS, XLAT, STI, and CLI commands

Part A INTERRUPT TIMING DIAGRAM

Part A: Prelab – Review the code in lab 3 A. asm – Fill in the blank comments beside the given code in provided spaces ; 8255 Setup CNTR_8255 EQU OUTPUT_MODE ; 8253 Setup COUNT_CNTR MODE 2 MODE 3 COUNT 0 COUNT 1 LOPT 1 MSEC HIPT 1 MSEC EQU … … … 0 FFFEH EQU EQU 00 H 0 B 5 H 000 EH 74 H 36 H 0008 H 000 AH 0 F 5 H ; Port control address ; Set up mode for port B output ; counter control register address ; __________________________________ ; counter 0 address ; counter 1 address ; __________________________________

Part A: Procedure • Download Lab 3 A. asm to the SDK (masm, link, exe 2 hex) and run it (sdk, GO FE 00: 0. , L <filename> , G ) • Understand what is happening. Hint: This program initializes a couple of counters, then runs in an infinite loop • Monitor the bus signals in the Logic Analyzer and copy INTR, /INTA waveforms from into your lab procedure handbook • Answer the questions in your report

Part B PROGRAMMING: TIMER, IC, DISPLAY

Part B: Prelab – Review the code in lab 3 B. asm and comment the code in the blanks provided (as part A) – Write the code section to implement ISR 2 which is timed using COUNT 2 (counter 2) – Write LED_TABLE for 0 -9 (use it in ISR 2) – How can you set ISR 2 to run at highest priority?

Part B: Procedure • Download Lab 3 B. asm given on the web to the SDK and run it as it is (do not modify yet). • This program generates a sawtooth waveform on the D/A converter and outputs a GARBAGE character to the rightmost digit of the SDK-86 display every second. Make sure it works properly before you modify the code • If everything works fine, modify Lab 3 B. asm according to your code to enable interrupt (ISR 2) that generates a counter (0 -9) in the leftmost digit of the SDK-86 display. The counter should count down from 9 to 0 and decrement every 0. 5 seconds. • Your new code must not interfere with the sawtooth or the GARBAGE character routines.

Hints • Review the code for Lab#1 part D – look in appropriate sections • Understand the use and syntax of LDS, XLAT, LED_TABLE • Understand the timer block diagram (8253) – Tutorial + Appendix B • How to access ports (control and data registers) – from lab 2

See you next week!