ELEC4601 Microprocessor systems Lab 4 Tutorial USART and
ELEC4601 Microprocessor systems Lab 4 Tutorial USART and Floating point Lab # 4 Part A 8251A (USART) and 8279 (LED Display) Part B 8087 Emulator Floating Point Multiplication
Suggested Readings Lab Manual: Lab # 4 SDK-86 Users Guide: Serial Interface (Section 2.11) Peripherals Handbook: 8251A, 8279, 8087 8086 User Manual: 8087 operation (Chap. 3) Online: IEEE 80-bit extended format for floating point
PART A USART AND DISPLAY Part A: Objectives Use of USART (Universal Synchronous/Asynchronous Receive Transmitter) - 8251A On SDK board, 8251A is used to communicate with PC (GO FE00:0.)
SDK board keypad controller 8279 8279 controls the SDK-86 boards keypad and display interface Given: SDK2PC subroutine Receives characters typed in on SDK keypad and transmits them to PC
Write: PC2SDK subroutine Characters typed on PC will be shown on the SDK-86 display Part A: PRELAB Complete PC2SDK subroutine in lab4a.asm Hints (see pseudo-code in Lab4a.asm): Use RxRDY_MASK to see if the USART receiver is ready (received any data) How to read the data in from USART? (IN command) Incoming data is in ASCII; use ASCII ranges to filter
unwanted data (characters that can not be displayed in the 7-segment display) Use the LED table (XLAT) for translation (7-segment) To handle unwanted data, show . How these procedures are evoked? PC2SDK PC2SDK SDK2PC
SDK2PC LED_TABLE is given (contains 0-9, A-F & .) You will need an ASCII code table (next page) Your code PC2SDK should do followings: 1) 2) 3) 4)
If a number (0-9) is pressed in PC, show it in SDK If a character among A-F is pressed, show it in SDK If anything else is pressed, show . in SDK Nothing is pressed, no change (exit procedure) Part A: Procedure Complete modifications to lab4a.asm Write PC2SDK subroutine (follow pseudo-code) Note: Characters received from the PC are in ASCII and must be translated into the 7-segment format for the SDK
display. Lab4a.asm already contains the translation table Hint: Use conditional jumping according to ranges of ASCII code of incoming data Use the mode and control bytes needed to program the 8279 and the 8251A Run the program and demo it to the TA PART B
FLOATING POINT OPERATION Part C: Objectives Lab4c.asm contains a floating point multiplication routine that emulates the 8087 The floating point numbers are stored in IEEE 80-bit format: sign-bit + 15-bit exponent + 64-bit mantissa The multiplication algorithm handles the exponent and fractional parts of the floating point numbers separately.
It treats the fraction part (64-bit mantissa) as four 16 bit words, multiplying each word in the multiplicand by each word in the multiplier. The final exponent (15-bit) result is simply the addition of the two input exponents with some adjustment for normalization. IEEE 80-bit extended format sign-bit + 15-bit exponent + 64-bit mantissa The numbers are normalized to the following format, where e
is the exponent and X is the mantissa: (-1)s * X * 2 e If S = 0, +ve If S = 1, -ve Mantissa (X) is in fraction format: X63*20 + X62*2-1 + X61*2-2 + X60*2-3 + X59*2-4 + X63-i*2-i + Actual exponent (e) is in Excess-N biasing format:
e = Exponent (214 1) Part C: PRELAB Review the code for lab4b.asm Bring a stopwatch for timing the programs Review extended precision IEEE floating point standard Consult online references Google for IEEE floating point format (80-bit) and how to decode it http://www.opferman.net/Text/ieee.txt
Part C Procedure Use MASM LAB4B.ASM /r, LINK LAB4B.OBJ, LAB4B.EXE DO NOT use ASSEM The result of the multiplication is displayed on the screen in 80-bit format. Convert into mantissa/exponent format and find the value You have to adjust the loop variables COUNT and COUNTA to get good execution times
How are COUNT and COUNTA related? Find the difference in execution times between the 8087 and the emulator (show to a TA) Discuss the difference between the two results See you next week!
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