15-01-2013, 04:05 PM
8085 MICROPROCESSOR
[attachment=47037]
INTRODUCTION
The Intel 8085 is an 8-bitmicroprocessor introduced by Intel in 1977. It was binary-compatible with the more-famous Intel 8080 but required less supporting hardware, thus allowing simpler and less expensive microcomputer systems to be built.
The "5" in the model number came from the fact that the 8085 requires only a +5-volt (V) power supply rather than the +5V, -5V and +12V supplies the 8080 needed. Both processors were sometimes used in computers running the CP/M operating system, and the 8085 later saw use as a microcontroller, by virtue of its low component count. Both designs were eclipsed for desktop computers by the compatible Zilog Z80, which took over most of the CP/M computer market as well as taking a share of the booming home computer market in the early-to-mid-1980s.
The 8085 had a long life as a controller. Once designed into such products as the DECtape controller and the VT100 video terminal in the late 1970s, it continued to serve for new production throughout the life span of those products (generally longer than the product life of desktop computers)
Features of 8085
1. 8085 is an 8-bit microprocessor.
2. The data word size of the 8085 microprocessor is 8-bits.Hence has 8-bit data bus.
3. The address size of 8085 microprocessor is 16-bits.Hence uses 16-bit address bus.It can directly process on 8-bits of data in single operation; hence it is known to be an 8-bit microprocessor.
4. It can directly address 216 = 65,536 bytes i.e., 64Kbytes (64 K memory locations) using 16-bits of address.
5. 8085 microprocessor is fabricated using NMOS technology and comes in an 40-pin DIP (dual-in-line)package.
6. It requires a single power supply of +5V.
7. It has provision of internal frequency generation when an crystal is connected between the specified pins.
8. The generated clock is divided by a factor of 2, hence to operate an 8085 based system at an frequency of 3 MHz, an crystal of 6 MHz frequency need to be connected to8085.
9. The enhanced version of 8085 is designed with HMOS transistors.
• The clock cycle of 8085 is of order of 320 ns.
• It has 80 basic instructions and 246 opcodes.
10. 8085 is enhanced version of its predecessor the 8080 microprocessor; thus its instruction set is upward compatible with that of 8080A, i.e., 8085 instruction set includes all the 8080A instructions plus some more instructions.
• But 8085 and 8080A are not pin compatible.
PIN Description
• 8085 is a 40 pin IC, DIP package. The signals from the pins can be grouped as follows
1. Power supply and clock signals
2. Address bus
3. Data bus
4. Control and status signals
5. Interrupts and externally initiated signals
6. Serial I/O ports
1. Power supply and clock signals
Vcc : + 5 volt power supply
Vss : Ground
X1, X2 : Crystal or R/C network or LC network connections to set the frequency of internal clock generator.The frequency is internally divided by two. Since the basic operating timing frequency is 3 MHz, a 6 MHz crystal is connected externally.
CLK (output)-Clock Output is used as the system clock for peripheral and devices interfaced with the microprocessor
Address Bus:
• A8 - A15 (output; 3-state)
• It carries the most significant 8 bits of the memory address or the 8 bits of the I/O address;
Multiplexed Address / Data Bus:
• AD0 - AD7 (input/output; 3-state)
• These multiplexed set of lines used to carry the lower order 8 bit address as well as data bus.
• During the opcode fetch operation, in the first clock cycle, the lines deliver the lower order address A0 - A7.
• In the subsequent IO / memory, read / write clock cycle the lines are used as data bus.
• The CPU may read or write out data through these lines.
INTERRUPT STRUCTURE 8085
• Interrupt is signals send by an external device to the processor, to request the processor to perform a particular task or work.
• Mainly in the microprocessor based system the interrupts are used for data transfer between the peripheral and the microprocessor.
• The processor will check the interrupts always at the 2nd T-state of last machine cycle.
•
• If there is any interrupt it accept the interrupt and send the INTA (active low) signal to the peripheral.
• The vectored address of particular interrupt is stored in program counter.
• The processor executes an interrupt service routine (ISR) addressed in program counter.
• It returned to main program by RET instruction.
[attachment=47037]
INTRODUCTION
The Intel 8085 is an 8-bitmicroprocessor introduced by Intel in 1977. It was binary-compatible with the more-famous Intel 8080 but required less supporting hardware, thus allowing simpler and less expensive microcomputer systems to be built.
The "5" in the model number came from the fact that the 8085 requires only a +5-volt (V) power supply rather than the +5V, -5V and +12V supplies the 8080 needed. Both processors were sometimes used in computers running the CP/M operating system, and the 8085 later saw use as a microcontroller, by virtue of its low component count. Both designs were eclipsed for desktop computers by the compatible Zilog Z80, which took over most of the CP/M computer market as well as taking a share of the booming home computer market in the early-to-mid-1980s.
The 8085 had a long life as a controller. Once designed into such products as the DECtape controller and the VT100 video terminal in the late 1970s, it continued to serve for new production throughout the life span of those products (generally longer than the product life of desktop computers)
Features of 8085
1. 8085 is an 8-bit microprocessor.
2. The data word size of the 8085 microprocessor is 8-bits.Hence has 8-bit data bus.
3. The address size of 8085 microprocessor is 16-bits.Hence uses 16-bit address bus.It can directly process on 8-bits of data in single operation; hence it is known to be an 8-bit microprocessor.
4. It can directly address 216 = 65,536 bytes i.e., 64Kbytes (64 K memory locations) using 16-bits of address.
5. 8085 microprocessor is fabricated using NMOS technology and comes in an 40-pin DIP (dual-in-line)package.
6. It requires a single power supply of +5V.
7. It has provision of internal frequency generation when an crystal is connected between the specified pins.
8. The generated clock is divided by a factor of 2, hence to operate an 8085 based system at an frequency of 3 MHz, an crystal of 6 MHz frequency need to be connected to8085.
9. The enhanced version of 8085 is designed with HMOS transistors.
• The clock cycle of 8085 is of order of 320 ns.
• It has 80 basic instructions and 246 opcodes.
10. 8085 is enhanced version of its predecessor the 8080 microprocessor; thus its instruction set is upward compatible with that of 8080A, i.e., 8085 instruction set includes all the 8080A instructions plus some more instructions.
• But 8085 and 8080A are not pin compatible.
PIN Description
• 8085 is a 40 pin IC, DIP package. The signals from the pins can be grouped as follows
1. Power supply and clock signals
2. Address bus
3. Data bus
4. Control and status signals
5. Interrupts and externally initiated signals
6. Serial I/O ports
1. Power supply and clock signals
Vcc : + 5 volt power supply
Vss : Ground
X1, X2 : Crystal or R/C network or LC network connections to set the frequency of internal clock generator.The frequency is internally divided by two. Since the basic operating timing frequency is 3 MHz, a 6 MHz crystal is connected externally.
CLK (output)-Clock Output is used as the system clock for peripheral and devices interfaced with the microprocessor
Address Bus:
• A8 - A15 (output; 3-state)
• It carries the most significant 8 bits of the memory address or the 8 bits of the I/O address;
Multiplexed Address / Data Bus:
• AD0 - AD7 (input/output; 3-state)
• These multiplexed set of lines used to carry the lower order 8 bit address as well as data bus.
• During the opcode fetch operation, in the first clock cycle, the lines deliver the lower order address A0 - A7.
• In the subsequent IO / memory, read / write clock cycle the lines are used as data bus.
• The CPU may read or write out data through these lines.
INTERRUPT STRUCTURE 8085
• Interrupt is signals send by an external device to the processor, to request the processor to perform a particular task or work.
• Mainly in the microprocessor based system the interrupts are used for data transfer between the peripheral and the microprocessor.
• The processor will check the interrupts always at the 2nd T-state of last machine cycle.
•
• If there is any interrupt it accept the interrupt and send the INTA (active low) signal to the peripheral.
• The vectored address of particular interrupt is stored in program counter.
• The processor executes an interrupt service routine (ISR) addressed in program counter.
• It returned to main program by RET instruction.