Page 108 - DCAP210_INTRODUCTION__TO_MICROPROCESSORS

Introduction to Microprocessors

Notes
Figure 7.6: Memory for the MCTS Project

Circuit Analysis
1. When the logic levels of A15-A12 are all 0, and the processor asserts MRE to read from
memory, the output O goes active and selects the chip. The address range of the EPROM is
0
as follows:
A15 A14 A13 A12 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 = 0000H

MSEL 0 ↓ ↓
1 1 1 1 1 1 1 1 1 1 1 1 = 0FFFH

2. The 6116 R/W memory is selected by the output signal of the decoder O2

A15 A14 A13 A12 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0

7.3 The 8085 MPU

The Microprocessor is a programmable logic device; designed with registers, flip flops, and timing
elements. The 8085 (8085A) is an 8 bit general purpose microprocessor capable of addressing 64K
of memory. It has 40 pins, requires a +5V single power supply, and can operate with a 3 MHz
single phase clock.
The 8085 is a complex IC of sequential circuits. The sequential circuits are designed to do some
operation depending on what is the input on their lines. The vital inputs on the lines are what
therefore determine what operation will be done by the sequential circuits inside it. Since we can
find a way to put different values of inputs to the input lines of the processor at different times,
we can make it execute different operations in a sequence that we desire. Thus, in other words we
can make the processor execute a programme to do useful things for us. These inputs then could
alternately, be called instructions. The inputs that we talked of so far are actually voltages to
represent 1s and 0s. They can only be 1s or 0s, they are called digital values. The number of input
lines that the processor provides are some estimation of the largeness of the instruction set that it
can support.
The 8085 has 8 bit input (actually called the input lines of the data bus), meaning that we could
8
have only a maximum of 2 = 256 different combination of 1s and 0s as inputs to the processor.
Well! The 8085 supports almost that many different instructions. The programme that we desire

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