SCHOTTKY BIPOLAR 8214

FUNCTIONAL DESCRIPTION

General

'he 8214 is a device specifically designed for use in real time, interrupt driven, microcomputer systems. Basically it is an eight (8) level priority control unit that can accept eight different interrupt requests, determine which has the highest priority, compare that level to a software maintained current status register and issue an interrupt to the system based on this comparison along with vector information to ind icate the location of the service routine.

Priority Encoder

The eight requests inputs, which are active low, come into the Priority Encoder. This circuit determines which request input is the most important (highest priority) as preassigned by the designer. (R7) is the highest priority input to the 8214 and (RO) is the lowest. The logic of the Priority En- coder is such that if two or more input levels arrive at the same time then the input having the highest priority will take presidence and a three bit output, corresponding to the act- ive level (modulo 8) will be sent out. The Priority Encoder also contains a latch to store the request input. This latch is controlled by the Interrupt Disable Flip-flop so that once an interrupt has been issued by the 8214 the request latch is no longer open. (Note that the latch does not store inact- ive requests. In order for a request to be monitored by the 8214 it must remain present until it has been serviced.)

Current Status Register

In an interrupt driven microcomputer system it is important to not only prioritize incom ing requests but to ascertain whether such a request is a higher priority than the interrupt currently being serviced.

The Current Status Register is a simple 4-bit latch that is treated as an addressable outport port by the microcom- puter system. It is loaded when the ECS input goes low.

Maintenance of the Current Status Register is performed as a portion of the service routine. Basically, when an interrupt is issued to the system the programmer outputs a binary code (modulo 8) that is the compliment of the interrupt level. This value is stored in the Current Status Register and is compared to all further prioritized incoming requests by the Priority Comparator. In essence, a copy of the cu rrent interrupt level is written into the 8214 to be used as a ref- erence for comparison. There is no restriction to this main- tenance, other level values can be written into this register as references so that groups of interrupt requests may be disallowed under complete control of the programmer.

Note that the fourth bit in the register is SGS. This input is part of the value written out by the programmer and per- forms a special function. The Priority Comparator will only issue an output that indicates the request level is greater than the Current Status Register. If both comparator inputs are equal to zero no output will be present. The SGS input allows the programmer to, in effect, disable this comparison and allow the 8214 to issue an interrupt to the system that is based only on the logic of the priority encoder.

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Intel 8080 manual Priority Encoder, Current Status Register
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8080 specifications

The Intel 8085 and 8080 microprocessors were groundbreaking innovations in the world of computing, paving the way for future microprocessor development and personal computing.

The Intel 8080, introduced in 1974, was an 8-bit microprocessor that played a fundamental role in the early days of personal computing. With a 16-bit address bus, it had the capability to address 64 KB of memory. Running at clock speeds of 2 MHz, the 8080 was notable for its instruction set, which included 78 instructions and 246 opcodes. It supported a range of addressing modes including direct, indirect, and register addressing. The 8080 was compatible with a variety of peripherals and played a crucial role in the development of many early computers.

The microprocessor's architecture was based on a simple and efficient design, making it accessible for hobbyists and engineers alike. It included an 8-bit accumulator, which allowed for data manipulation and storage during processing. Additionally, the 8080 featured registers like the program counter and stack pointer, which facilitated program flow control and data management. Its ability to handle interrupts also made it suitable for multitasking applications.

The Intel 8085, introduced in 1976, was an enhancement of the 8080 microprocessor. It maintained a similar architecture but included several key improvements. Notably, the 8085 had a built-in clock oscillator, simplifying system design by eliminating the need for external clock circuitry. It also featured a 5-bit control signal for status line management, which allowed for more flexible interfacing with peripheral devices. The 8085 was capable of running at speeds of up to 3 MHz and had an extended instruction set with 74 instructions.

One of the standout features of the 8085 was its support for 5 extra instructions for stack manipulation and I/O operations, which optimized the programming process. Additionally, it supported serial communication, making it suitable for interfacing with external devices. Its 16-bit address bus retained the 64 KB memory addressing capability of its predecessor.

Both the 8080 and 8085 microprocessors laid the groundwork for more advanced microprocessors in the years that followed. They demonstrated the potential of integrated circuits in computing and influenced the design and architecture of subsequent Intel microprocessors. Their legacy endures in the way they revolutionized computing, making technology accessible to a broader audience, and their influence is still felt in the design and architecture of modern microprocessors today.
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