* start read/write:
* (1<<TWEN)|(1<<TWIE)|(1<<TWINT)|(1<<TWSTA)
* (1<<TWEN)|(1<<TWIE)|(1<<TWINT)|(1<<TWSTA)
* (1<<TWEN)|(1<<TWIE)|(1<<TWINT)|(1<<TWSTA)
* (1<<TWEN)|(1<<TWIE)|(1<<TWINT)|(1<<TWSTA)
* start read/write:
* (1<<TWEN)|(1<<TWIE)|(1<<TWINT)|(1<<TWSTA)
* (1<<TWEN)|(1<<TWIE)|(1<<TWINT)|(1<<TWSTA)
* (1<<TWEN)|(1<<TWIE)|(1<<TWINT)|(1<<TWSTA)
* (1<<TWEN)|(1<<TWIE)|(1<<TWINT)|(1<<TWSTA)