What is the difference between the numbers enclosed and not enclosed?

If the number is enclosed in angle brackets above the bit name, this means that the bit name is defined as a bit SFR by the device file. This means that the name can be used in a program. (Please refer to How to Use This Manual > How to Read This Manual > How to interpret the register format in the hardware manual.)

For example, the ADCEN bit located at bit 5 of the PER0 register can be used as-is in a program.

SET1 ADCEN ; Supply clock to A/D converter (assembler statement)

ADCEN = 1; // Supply clock to A/D converter (C statement)

A bit defined as a bit SFR is an SFR for which bit manipulation is allowed, and the bit has meaning by itself. A program is easier to read when bit names are used instead of bit numbers which are almost meaningless (for example, SFR for interrupt).

SET1 ADMK ; A/D converter interrupt mask (assembler statement)

ADMK = 1; // A/D converter interrupt mask (C statement)

It also makes code porting easier in cases where the bit position (number) changes between subseries. (Example: MK1H.0 in G13 and G14 is MK1L.2 in G12 and MK01H.1 in G10. If you use ADMK, there is no need to change the code.)