EL21C Class Test #2 --- 20th November 2002

Duration: 1 Hour --- Attempt ALL questions.

( 1 ) Sketch the waveform of an asynchronous serial transmission

of the ASCII character, 4EH. Label the following aspects of

the waveform: start bit; least significant bit (lsb); most

significant bit (msb);stop bit; parity bit; bit-period

(Use Even parity;56.6K baud; 8-data bits; 1-stop bit). [7]

( 2 ) The first 8155 PPI on the SDK-85 kit is allocated port #'s

from 20H(CSR) and is driven by a 1.0 MHz clock. Write an

instruction sequence to:

(a) Start the Timer [2]

(b) Load the Timer with a value which will produce a delay

of 100 μs then 'fire' a single pulse & repeat. [2]

(c) Stop the Timer [2]

(d) What are the maximum & minimum delay times ? [2]

( 3 ) An A/D converter, with four channels, is to interface to

the SDK-85 kit. Using any ports at your disposal, sketch a

diagram showing how you would control this A/D [ Label and

describe all signals you use.] [6]

( 4 ) Explain the various steps executed by the 8085 CPU

microprocessor when an interrupt occurs, until it returns to

the next instruction [ use any of the hardware interrupts to

illustrate your answer.] [5]

( 5 ) How does the 8085 CPU distinguish between memory address

0036H and port address 36H ? [3]

( 6 ) How is the instruction SIM used in serial communication?[2]

( 7 ) Figure 1 shows the main address decoder for an 8085 CPU

based computer. Determine the address ranges of the

3:8 decoder. [4]

Bonus: What is the colour of the 8 x LED’s interfaced to

Port 00H on the SDK-85 kit in the Lab?