i have check more than 6 "siemens C55 "cell phone to use MC 8051,, but when ever i connect it with hyper terminal to check for AT command it get OFF,,,when i click on call in hyper terminal it get off,, ,i checked many cell phones but all have sam prob ,, plzzz help.........
one is normal serial port cable, it has no any problem when connected to HyperTerminal.
and other one is USB to Serial cable, this last cable has trouble with HyperTerminal.
i have cable , which is not orignal, and its is RS232 (DB-9) connector.,, i think the wires in this cable are direct connected and NO voltage convertor is there ,, if i connect i this way as shown in figure then , will cell phone work properly with hyperterminal ???
Your cable can't connect your cellphone to PC properly.
PC COM port is a RS232 port, that mean recoqnize voltage <-5 Volt as logical '1' and voltage >+5 Volt as loginal '0'
Cellphone serial port is low voltage digital device, voltage >2 Volt as '1' and <8 Volt as '0'
You have to use Voltage Converter to interface cellphone to PC, one of the circuit is :
Note : ignore MBUS from above circuit