in a powerup rs232 step 202 the processing unit enters this sequence 200 when a connection to an external device i e desktop computer is detected in the powerup rs232 step 202 a serial line buffer not shown is supplied with power the sequence 200 then proceeds to a wait step 204 the processing unit waits for a specific period of time in the order of milliseconds so that the serial line buffer may properly receive power supply and generate appropriate signals after the wait step 204 the sequence 200 proceeds to a cts signal detected decision step 206 where the processing unit detects the presence or absence of a clear to send cts signal a cts signal is a rs 232 signal sent from a receiving device to a transmitting device indicating that it is clear to send data cts signal is asserted by the receiving device when asserted it indicates that the receiving device is ready to accept serial data when unasserted it indicates that data transmission should be disabled if the presence of a cts signal is detected the sequence 200 proceeds to a powerdown step 210 a where power is withdrawn from the serial line buffer the connection type is determined to be serial and the sequence then proceeds to a is serial connection step 301 in sequence 300 if the absence of a cts signal is detected the sequence 200 proceeds to a is it 5v decision step 208 a usb connection typically draws a 5 volt power while.