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When bit 15 of the opcode is set, it indicates that the 8-bit operand address in opcode bits 0–6 and 14 is extended to 16 bits using bits 0–7 of the following instruction word. Such instructions are written with an L prefix (LADD vs. ADD) and take an extra cycle to execute.
Adding BCD numbers using these opcodes is a complex task, and requires many instructions to add even modest numbers. It can also require a large amount of memory. [2] If only doing integer calculations, then all integer calculations are exact, so the radix of the number representation is not important for accuracy.
Fetching the instruction opcodes from program memory well in advance is known as prefetching and it is served by using a prefetch input queue (PIQ). The pre-fetched instructions are stored in a queue. The fetching of opcodes well in advance, prior to their need for execution, increases the overall efficiency of the processor boosting its speed ...
New opcodes that introduced new functionality (e.g. SHLD, SETcc) For instruction forms where the operand size can be inferred from the instruction's arguments (e.g. ADD EAX,EBX can be inferred to have a 32-bit OperandSize due to its use of EAX as an argument), new instruction mnemonics are not needed and not provided.
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.
Opcode abbreviated from operation code is the portion of a machine language instruction that specifies the operation to be performed. Base instructions form a Turing-complete instruction set. Object model instructions provide an implementation for the Common Type System.
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