Microprocessor 8085 i
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Microprocessor 8085 Junied Khalid Khan EDUCREATION PUBLISHING (Since 2011) www.educreation.in iii
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Junied Khalid Khan 1. Introduction Microprocessor is an electronic integrated chip (IC) that has computing and decision making ability. In otherwords, microprocessor is an electronic IC that fetches (reads) instructions from memory, execute them and provide results. Number of data bits executed in one machine cycle is known as a bit of microprocessor. Microprocessor 8085 is an 8-bit microprocessor designed by intel in 1977 using NMOS technology and requires +5 V supply and 3MHZ frequency to operate. Microcomputer is a combination of microprocessor, memory and input/output. If all tasks of a CPU are performed by microprocessor than such type of computer is known as microcomputer. Moreover, microcontroller is a microcomputer on a single chip. It is an example of ASIC (Application Specific Integrated Chip) design. Microprocessor contains hardware and software. Software is ROM (Read only Memory) which is an integral part of microprocessor and all system related information is stored in it. ROM comes into the picture at the time of power switch condition. On the other hand RAM (Random Access Memory) is externally interfaced with microprocessor. All instructions and commands are fed into it. Some important terms: Bus: is a group of wires (or parallel combination) that is used for interfacing between two devices. It can be both unidirectional and bidirectional. 1
Microprocessor 8085 Machine Language: If commands and instructions are written in binary pattern than such type of language is known as machine language. It is platform dependent and machine specific language. For example language written for a robot. Assembly Language: In assembly language binary pattern is replaced by english like words called mnemonics. It is also platform dependent or machine specific. Fig 1.1 Assembler: is basically a translator that converts assembly language into machine language. It is a software. If translation task is performed manually than it is known as hand assembly. Compiler: reads program at once from source code, produces its object code that is executed by processor. It is a software mostly used in C, C++. Interpreter: is a software that reads one instruction at a time from source code, produces its object code that is executed by processor before reading next instruction. Low Level Language: All platform or machine specific languages are known as low level language. For example machine language, assembly language. High Level Language: All platform independent languages are known as high level language. For example C, C++, Java etc. Fig 1.2 2
Junied Khalid Khan Faster Execution Require Large Memory to Store Easier Debugging Machine High level language High level language language Assembly language Assembly language Assembly language High level language Machine language Machine Language Table 1.1 Characteristics of different languages Microprocessor Bit of Microprocessor Technology used 4004 4 bit PMOS 8008 8 bit NMOS 8080 8 bit NMOS 8085 8 bit NMOS 8086 16 bit HMOS 80186 16 bit BICMOS 80206 16 bit BICMOS 80306 32 bit BICMOS 80406 32 bit BICMOS 80586 Pentium 64 bit BICMOS Pentium Pro BICMOS P II BICMOS P III BICMOS P IV BICMOS Dual core Core to dual i series (i3, i5, i7, i9...) Table 1.2 Details of different microprocessors Microprocessor 8085 is an advanced version of 8080 microprocessor with backward compatibility. Instruction set of 3
Microprocessor 8085 8085 is an instruction set of 8080 plus RIM (Read Interrupt Mask) and SIM (Set Interrupt Mask). Speed of microprocessor is directly proportional to frequency and frequency is directly proportional to bits of microprocessor. ***** 4
Junied Khalid Khan 2. Architecture of 8085 Microprocessor There are two types of architecture: i. External architecture ii. Internal architecture External Architecture Microprocessor 8085 consists of 40 pins in which pin 20 denotes ground pin. All 40 pins are divided into 6 categories as per their function. Fig 2.1 Pin diagram of 8085 microprocessor 5
Microprocessor 8085 1. Address Pin: They are 16 in number (A15-A8 & A7-A0). 2. Data Pin: They are 8 in number. Lower byte of address pins also work as data pins (A7-A0). 3. Control and status pin: It consists of following: : For input 1, microprocessor communicates to I/0 and if input is 0, microprocessor communicates to memory. Fig 2.2 S i & S o : By measuring this pin we can find out which machine cycle is going on inside the microprocessor. = 0 Write operation is performed on input 0. = 0 Read operation is performed on input 0. But only one operation is performed at a time or. Address Latch Enable (ALE): 8085 processor has 16 address lines for 16 bit address of a memory location. Out of this 16 address lines 8 address lines are solely dedicated to transfer 8 higher order address bits while the remaining lower order 8 bits of the address are sent through another 8 lines multiplexed with the 8 bit data lines. It is the control signal ALE to be sent by the processor in appropriate time to indicate the operation of this 8 bit multiplexed bus whether it will be used to send the lower order 8 address bits or to send the 8 data bits. Making ALE control HIGH the multiplexed 8 bit bus will 6
Junied Khalid Khan act as address bus while making ALE control LOW the same 8 bit multiplexed bus will act as data bus. Thus, ALE = 1 makes the address latched i.e. latch enable and ALE = 0 makes the address bus disable but making it data bus enable. Fig 2.3 Address Latch Enable Flip-Flop is a cross-coupled device which can store maximum of 1 bit. It is edge triggered. Whereas a latch is one of the applications of flip-flop and is level triggered. 4. Frequency and Power Supply Pin: To get 3MHZ frequency 6MHZ crystal oscillator is connected between X1 and X2 and internally divided by 2 to get 3MHZ clockpulse. It also requires +5 V supply to operate. Fig 2.4 7
Microprocessor 8085 5. Serial Data Transfer Pin: There are two instructions in serial data transfer: SID: Serial Input Data by use of RIM instruction. SOD: Serial Output Data by use of SIM instruction. We will discuss RIM and SIM instructions further in detail. 6. Externally Initiated Signal Pins: There are several categories: Interrupts: They are TRAP, RST 7.5, RST 6.5, RST 5.5, INTR or RST 4.5 HOLD: This pin is used in Direct Memory Access (DMA). Ready Pin: With the help of this pin slower peripherals interface with microprocessor. Fig 2.5 RESET Pin: It resets the microprocessor. In 8085 microprocessor 5 pins are active low;,,,. Number of pins in outward direction are 27 and number of pins in inward direction are 21. Memory capacity of microprocessor is represented by 2 n d where n is address pin and d is data pin. Memory word size can be defined as the maximum bit of information that can be stored at a particular memory location. 8
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