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The SDK-85 MCS-85 System Design Kit was a single board microcomputer system kit using the Intel 8085 processor, clocked at 3 MHz with a 1.3 μs instruction cycle time. It contained all components required to complete construction of the kit, including LED display, keyboard, resistors, caps, crystal, and miscellaneous hardware.
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.
Below is the full 8086/8088 instruction set of Intel (81 instructions total). [2] These instructions are also available in 32-bit mode, in which they operate on 32-bit registers (eax, ebx, etc.) and values instead of their 16-bit (ax, bx, etc.) counterparts.
This allowed the use of the Intel 8085's RIM and SIM instructions to read the level on the SID and set the level on SOD line. What was so unique about this implementation was that after resetting the Explorer 85, the user had to press the space bar on the attached computer terminal .
The instruction set architecture (ISA) that the computer final version (SAP-3) is designed to implement is patterned after and upward compatible with the ISA of the Intel 8080/8085 microprocessor family. Therefore, the instructions implemented in the three SAP computer variations are, in each case, a subset of the 8080/8085 instructions.
For a floating-point add or subtract operation, the significands of the two numbers must be aligned, which requires shifting the smaller number to the right, increasing its exponent, until it matches the exponent of the larger number. This is done by subtracting the exponents and using the barrel shifter to shift the smaller number to the right ...
For most instructions that accept a ModR/M byte, encodings with the SIB byte will result in the computation of a single effective address as (scale * index) + base + displacement as described above. However, some newer x86 instruction set extensions have added instructions that use the SIB byte in other, more specialized ways: VSIB addressing ...
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.