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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.
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 Intel 8279 is a keyboard and display controller developed for interfacing to Intel 8085, 8086 and 8088 microprocessors. The industrial version of ID8279 was available for USD $30.70 in quantities of 100. [1] Its important features are: [2] Simultaneous keyboard and display operations. Scanned keyboard mode.
One use for such "packed" structures is to conserve memory. For example, a structure containing a single byte (such as a char) and a four-byte integer (such as uint32_t) would require three additional bytes of padding. A large array of such structures would use 37.5% less memory if they are packed, although accessing each structure might take ...
The 8255 has a similar function to the Motorola 6820 PIA (Peripheral Interface Adapter) from the Motorola 6800 family, also originally packaged as 40-pin DIL. The 8255 provides 24 I/O pins with four programmable direction bits: one for Port A(7:0) (i.e., all pins in the port), one for Port B(7:0), one for Port C(3:0) and one for Port C(7:4).
In contrast, in direct memory access (DMA) operations, the CPU is uninvolved in the data transfer. The term can refer to either memory-mapped I/O (MMIO) or port-mapped I/O (PMIO). PMIO refers to transfers using a special address space outside of normal memory, usually accessed with dedicated instructions, such as IN and OUT in x86 architectures.
As the Execution Unit is executing the current instruction, the bus interface unit reads up to six (or four) bytes of opcodes in advance from the memory. The queue lengths were chosen based on simulation studies. [9] An exception is encountered when the execution unit encounters a branch instruction i.e. either a jump or a call instruction. In ...
The 8259 may be configured to work with an 8080/8085 or an 8086/8088. On the 8086/8088, the interrupt controller will provide an interrupt number on the data bus when an interrupt occurs. The interrupt cycle of the 8080/8085 will issue three bytes on the data bus (corresponding to a CALL instruction in the 8080/8085 instruction set).