Features of Intel 8085 microprocessor

Features of Intel 8085 microprocessor:

The features of Intel 8085 microprocessor are as follows:

Breadboard Atmel AVR microprocessor project.
Breadboard Atmel AVR microprocessor project. (Photo credit: thepodger)

1) 8085 microprocessor is an 8-bit microprocessor. I.e. it can accept or provide 8-bit data simultaneously.

2) 8085 microprocessor is a single chip, NMOS device implemented with 6200 transistors.

3) 8085 microprocessor requires a single +5V DC power supply.

4) 8085 microprocessor provides on-chip clock generator, therefore there is no need of external clock generator, but it requires external tuned circuit like LC, RC or crystal.

5) 8085 microprocessor requires two-phase, 50% duty cycle, TTL clock. These clock signals are generated by an internal clock generator (refer to the following figure).

2 Phase TTL clock

6) The maximum clock frequency of 8085 microprocessors is 3MHz whereas minimum clock frequency is 500 KHz.

7) 8085 provides 74 instructions with the following addressing modes:
a. register
b. direct
c. immediate
d. indirect
e. implied.

8) The data bus is multiplexed with the address bus, hence it requires external hardware to separate data lines from address lines (this is one of the disadvantages of 8085).

9) 8085 microprocessor provides 16 address lines, therefore it can access 2^16 = 64K bytes of memory.

10) It generates 8 bit I/O address, hence it can access 2^8 = 256 input ports and 256 output ports.

11) It performs the following arithmetic and logical operations.
a. 8-bit, 16-bit binary addition
b. 2-digit BCD addition
c. 8-bit binary subtraction
d. logical AND, OR, EXOR
e. complement and shift operations.

12) 8085 microprocessor has five hardware interrupts: TRAP, RST 5.5, RST 6.5, RST 7.5, INTR

13) The hardware interrupt capability of 8085 microprocessor can be increased by providing external hardware.

14) 8085 microprocessor has the capability to share its bus with external bus controller (direct memory access controller); for transferring a large amount of data from memory to I/O and vice versa.

15) 8085 microprocessor provides one accumulator, one flag register, 6 general purpose registers, and two special purpose registers.

16) It provides status for advanced control signals. (Advanced control signals are used in large systems).

17) 8085 microprocessor can be used to implement three chip microcomputer (8085, 8155, 8355)

18) 8085 microprocessor provides two serial I/O lines which are SOD and SID; it means, serial peripherals can be interfaced with 8085 microprocessor directly.

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Classification of Memory in computer

Classification of memory

This section provides a classification of memories. There are two main types of memories i.e. RAM and ROM. Following tree diagram shows the classification of Memory:

Classification of memory
Classification of memory

ROM (Read Only Memory):

The first classification of memory is ROM. The data in this memory can only be read, no writing is allowed. It is used to store permanent programs. It is a nonvolatile type of memory. The classification of ROM memory is as follows:

a) Masked ROM: the program or data are permanently installed at the time of manufacturing as per requirement. The data can not be altered. The process of permanent recording is expensive but economic for large quantities.

b) PROM (Programmable Read Only Memory): The basic function is same as that of masked ROM. but in PROM, we have fuse links. Depending upon the bit pattern, the fuse can be burnt or kept intact. This job is performed by PROM programmer.

To do this, it uses high current pulse between two lines. Because of high current, the fuse will get burnt; effectively making two lines open. Once a PROM is programmed we cannot change connections, only a facility provided over masked ROM is, the user can load his program in it. The disadvantage is a chance of regrowing of the fuse and changes the programmed data because of aging.

c) EPROM (Erasable Programmable Read Only Memory): the EPROM is programmable by the user. It uses MOS circuitry to store data. They store 1’s and 0’s in form of charge. The information stored can be erased by exposing the memory to ultraviolet light which erases the data stored in all memory locations. For ultraviolet light, a quartz window is provided which is covered during normal operation. Upon erasing it can be reprogrammed by using EPROM programmer. This type of memory is used in a project developed and for experiment use. The advantage is it can be programmed erased and reprogrammed. The disadvantage is all the data get erased even if you want to change single data bit.

d) EEPROM: EEPROM stands for Electrically erasable programmable read only memory. This is similar to EPROM except that the erasing is done by electrical signals instead of ultraviolet light. The main advantage is the memory location can be selectively erased and reprogrammed. But the manufacturing process is complex and expensive so do not commonly used.

RAM (Random Access Memory):

The second classification of memory is RAM. The RAM is also called as read/write memory. The RAM is a volatile type of memory. It allows the programmer to read or write data. If the user wants to check the execution of any program, user feeds the program in RAM memory and executes it. The result of execution is then checked by either reading memory location contents or by register contents.

Following is the classification of RAM memory. It is available in two types:

a) SRAM (Static RAM): SRAM consists of the flip-flop; using either transistor or MOS. for each bit we require one flip-flop. Bit status will remain as it is; unless and until you perform next write operation or power supply is switched off.

Advantages of SRAM:

  • Fast memory (less access time)
  • Refreshing circuit is not required.

Disadvantages of SRAM:

  • Low package density
  • Costly

b) DRAM (Dynamic RAM): In this type of memory a data is stored in form of charge in capacitors. When data is 1, the capacitor will be charged and if data is 0, the capacitor will not be charged. Because of capacitor leakage currents, the data will not be held by these cells. So the DRAMs require refreshing of memory cells. It is a process in which same data is read and written after a fixed interval.

Advantages of DRAM:

  • High package density
  • Low cost

Disadvantages of DRAM:

  • Required refreshing circuit to maintain or refresh charge on the capacitor, every after few milliseconds.

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