We haven't had an opportunity to verify or disprove this report, so we present it to the world as "additional information. standard 8051 Program and data memory share the same address space but are accessed via different instruction types The memory organisation of C8051F93x is very similar to that of the basic 8051, especially the internal data memory and its layout in terms of register banks, bit-addressable space and location of SFRs. In this case, it would be a three-byte instruction. Note: We received input from an user that the undefined instruction really has a format of Undefined bit1,bit2 and effectively copies the value of bit2 to bit1. However, based on my research, executing this undefined instruction takes 1 machine cycle and appears to have no effect on the system except that the Carry Bit always seems to be set. As we know Microprocessor like 8085, Z-80 or M6800 contains the ALU, control unit and some registers, but there were no internal storages. It is a very famous Microcontroller of Intel family. Since it is not documented nor defined it is not recommended that it be executed. More Detail The 8051 Microcontroller is designed by Intel in 1981. The 8051 supports 255 instructions and OpCode 0xA5 is the single OpCode that is not used by any documented function. Description: The "Undefined" instruction is, as the name suggests, not a documented instruction.
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