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The Intel 8085 ("eighty-eighty-five") is an 8-bit microprocessor produced by Intel and introduced in March 1976. [2] It is the last 8-bit microprocessor developed by Intel. It is software-binary compatible with the more-famous Intel 8080 with only two minor instructions added to support its added interrupt and serial input/output features.
An address decoder is a particular use of a binary decoder circuit known as a "demultiplexer" or "demux" (the 74154 is commonly called a "4-to-16 demultiplexer"), which has many other uses besides address decoding. Address decoders are fundamental building blocks for systems that use buses.
Memory-mapped I/O is preferred in IA-32 and x86-64 based architectures because the instructions that perform port-based I/O are limited to one register: EAX, AX, and AL are the only registers that data can be moved into or out of, and either a byte-sized immediate value in the instruction or a value in register DX determines which port is the source or destination port of the transfer.
The reset vector for 6502 processor family is a 16-bit address stored at 0xFFFC and 0xFFFD. The reset vector for 6800 and 6809 processor families is a 16-bit address stored at 0xFFFE and 0xFFFF. No Reset Vector. For 8051 / 8080 / 8085 / Z80, reset starts code execution at address 0x0000.
Modern processors can even do some of the steps out of order as decoding on several instructions is done in parallel. Decoding the op-code in the instruction register includes determining the instruction, determining where its operands are in memory, retrieving the operands from memory, allocating processor resources to execute the command (in ...
The PCI device is required to decode only the lowest order 11 bits of the address space (AD[10] to AD[0]) address/data signals, and can ignore decoding the 21 high order A/D signals (AD[31] to AD[11]) because a Configuration Space access implementation has each slot's IDSEL pin connected to a different high order address/data line AD[11 ...
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While the execution unit is decoding or executing an instruction which does not require the use of the data and address buses, the bus interface unit fetches instruction opcodes from the memory. This process is much faster than sending out an address, reading the opcode and then decoding and executing it.