HC05 Datasheet, PDF (6/232 Pages) Motorola, Inc – High-density complementary metal oxide semiconductor (HCMOS) microcontroller unit

Conventions
Where abbreviations are used in the text, an explanation can be found in the
glossary, at the back of this manual. Register and bit mnemonics are defined in the
paragraphs describing them.
An overbar is used to designate an active-low signal, eg: RESET.
Unless otherwise stated, a shaded cell in a register diagram indicates that the bit is
either unused or reserved; ‘u’ is used to indicate an undefined state (on reset).
Unless otherwise stated, a pin labelled as ‘NU’ should be tied to V_SS in an electrically
noisy environment. Pins labelled ‘NC’ can be left floating, since they are not bonded
to any part of the device.