The port register consists of 8 bits, and bit 0 to bit 8 are associated with each port number.
For example, if you want to set P1.0 and P1.6, you need to set bits 0 and 6 of register P1OUT, which sets the output High/Low of ports 1.0 to 1.7.

In the microcomputer program, the numerical value that sets the register is defined by function and content, such as BIT0 (= 00000001), so that the user can understand the program by looking at it, so the program is written like P1OUT |= BIT0 + BIT6 I will describe. Since the ORed value of 00000001 and 01000000 is inserted into the register P1OUT, it becomes 01000001.