04-05-2013, 12:28 PM
Introduction to 8085 Microprocessor
[attachment=53420]
INTRODUCTION
Intel 8085 microprocessor is the next generation of Intel 8080 CPU family. In addition to being faster than the 8080, the 8085 had the following enhancements:
• Intel 8085 had single 5 Volt power supply.
• Clock oscillator and system controller were integrated on the chip.
• The CPU included serial I/O port.
• Two new instructions were added to 8085 instruction set.
The CPU also included a few undocumented instructions. These instructions were supposed to be a part of the CPU instruction set, but at the last moment they were left undocumented because they were not compatible with forthcoming Intel 8086.
Full list of differences between Intel 8080 and 8085 processors.
There were multiple versions of 8085 microprocessors. The original version of the 8085 microprocessor without suffix "A" was manufactured by Intel only, and was very quickly replaced with 8085A containing bug fixes. A few years after that, around 1980, Intel introduced 8085AH - HMOS version of 8085A. There was also 80C85A - CMOS version of the 8085A. It's not clear if 80C85 was ever manufactured by Intel or not, but it was produced by at least two second source manufacturers - OKI and Tundra Semiconductor. Tundra Semiconductor manufactured the fastest 8085 microprocessor running at 8 MHz.
Second source manufacturers: AMD, Mitsubishi, NEC, OKI, Siemens, Toshiba. Soviet Union also manufactured clones of Intel 8085 CPU.
The 8085 Microprocessor
The INTEL 8085 microprocessor. This chip was the last 8-bit general purpose CPU made by INTEL and has 40 pins.
The address bus requires 16 pins and the data bus requires 8 pins but INTEL cleverly decided to share or multiplex these two busses so the data bus share the lower (A0-A7) 8 pins of the address bus. This caused no problem since address and data are never on the bus at the same time.
Two pins are for serial communications with the 8085. Through these pins, serial data can be sent or received with another computer. This is how we will load a program into the 8085 kit used in the lab, from a PC.
Five more pins are for a different kind of input called interrupts. In our example in lesson 1 of the program where we are standing at the street corner, watching the light and the traffic, if a person walked up and tapped us on the shoulder and asked what time it is, this would be an example of an interrupt. It doesn't alter the program we are doing, it just temporarily stops us while we tell the time to the person. As soon as we tell the time, we go back to watching the lights and traffic as before. This describes the action of an interrupt.
The interrupt has a program associated with it to guide the micro through a problem. In the case of the above example, this program would be to look at our watch, read the time, and then tell it to the person. This is called an interrupt service routine (ISR). Each time an interrupt occurs, the current program is temporarily stopped and the service routine is executed and when complete, returns to the current program. We will spend a lot more time later describing interrupts and how we'll use them.
Inside the 8085 there are 10 seperate registers. They are called A, B, C, D, E, H, L, PSW, PC, and SP. All but the PSW, PC, and SP registers are used for temporary storage of whatever is needed by the program. The accumulator called A is also different from the other registers. It is used to accumulate the results of various instructions like add or sub (subtract). The Program Counter (PC) we have already mentioned while the Stack Pointer (SP) actually holds addresses and is 16 bits wide. All the others are 8 bits wide.
There are other features to be covered later, as they come up. In the next lesson we will start looking at assembly language, the method we will use to write a program.
[attachment=53420]
INTRODUCTION
Intel 8085 microprocessor is the next generation of Intel 8080 CPU family. In addition to being faster than the 8080, the 8085 had the following enhancements:
• Intel 8085 had single 5 Volt power supply.
• Clock oscillator and system controller were integrated on the chip.
• The CPU included serial I/O port.
• Two new instructions were added to 8085 instruction set.
The CPU also included a few undocumented instructions. These instructions were supposed to be a part of the CPU instruction set, but at the last moment they were left undocumented because they were not compatible with forthcoming Intel 8086.
Full list of differences between Intel 8080 and 8085 processors.
There were multiple versions of 8085 microprocessors. The original version of the 8085 microprocessor without suffix "A" was manufactured by Intel only, and was very quickly replaced with 8085A containing bug fixes. A few years after that, around 1980, Intel introduced 8085AH - HMOS version of 8085A. There was also 80C85A - CMOS version of the 8085A. It's not clear if 80C85 was ever manufactured by Intel or not, but it was produced by at least two second source manufacturers - OKI and Tundra Semiconductor. Tundra Semiconductor manufactured the fastest 8085 microprocessor running at 8 MHz.
Second source manufacturers: AMD, Mitsubishi, NEC, OKI, Siemens, Toshiba. Soviet Union also manufactured clones of Intel 8085 CPU.
The 8085 Microprocessor
The INTEL 8085 microprocessor. This chip was the last 8-bit general purpose CPU made by INTEL and has 40 pins.
The address bus requires 16 pins and the data bus requires 8 pins but INTEL cleverly decided to share or multiplex these two busses so the data bus share the lower (A0-A7) 8 pins of the address bus. This caused no problem since address and data are never on the bus at the same time.
Two pins are for serial communications with the 8085. Through these pins, serial data can be sent or received with another computer. This is how we will load a program into the 8085 kit used in the lab, from a PC.
Five more pins are for a different kind of input called interrupts. In our example in lesson 1 of the program where we are standing at the street corner, watching the light and the traffic, if a person walked up and tapped us on the shoulder and asked what time it is, this would be an example of an interrupt. It doesn't alter the program we are doing, it just temporarily stops us while we tell the time to the person. As soon as we tell the time, we go back to watching the lights and traffic as before. This describes the action of an interrupt.
The interrupt has a program associated with it to guide the micro through a problem. In the case of the above example, this program would be to look at our watch, read the time, and then tell it to the person. This is called an interrupt service routine (ISR). Each time an interrupt occurs, the current program is temporarily stopped and the service routine is executed and when complete, returns to the current program. We will spend a lot more time later describing interrupts and how we'll use them.
Inside the 8085 there are 10 seperate registers. They are called A, B, C, D, E, H, L, PSW, PC, and SP. All but the PSW, PC, and SP registers are used for temporary storage of whatever is needed by the program. The accumulator called A is also different from the other registers. It is used to accumulate the results of various instructions like add or sub (subtract). The Program Counter (PC) we have already mentioned while the Stack Pointer (SP) actually holds addresses and is 16 bits wide. All the others are 8 bits wide.
There are other features to be covered later, as they come up. In the next lesson we will start looking at assembly language, the method we will use to write a program.