What are the characteristics of the instruction system of the 8051 microcontroller?

The instruction system of 8051 consists of 111 instructions. If classified by the number of bytes, there are 49 single-byte instructions, 46 double-byte instructions and 16 three-byte instructions, with single-byte instructions being the main ones; if classified by the instruction execution time, there are 64 single-cycle instructions, 45 double-cycle instructions and 2 four-cycle instructions, with single-cycle instructions being the main ones. 
The instruction system of 8051 has the following characteristics: 
(1) High storage efficiency and fast execution speed. It can perform direct address to direct address data transfer and can transfer the content of a parallel I/O port to the internal RAM unit without passing through accumulator A or working register Rn. This can greatly improve the transfer speed and alleviate the bottleneck effect of accumulator A. 
(2) Use the indexed addressing mode to access the table in the program memory and transfer the fixed constant or table byte content in the program memory unit to accumulator A. This provides convenience for compiling translation algorithms. 
(3) There are multiplication and division instructions in the arithmetic operation instructions. 
(4) Some instructions in the instruction system that operate on the I/O port have the function of "read-modify-write". This function means that when executing the instruction to read the latch, the CPU first completes the value of the latch through the buffer BUF2 to enter the internal, modify and change it, and then rewrite it to the latch. This type of instruction includes all logical operations and bit operation instructions.  
(5) There is a Boolean processor inside the 8051 microcontroller, which has a rich bit operation instruction for the address space. There are 17 Boolean operation instructions, including Boolean transfer instructions, Boolean state control instructions, Boolean logic operation instructions, and Boolean conditional transfer instructions.