Hello.

I want to interfacing SIEMENS C35i or compatible mobile phone with the AT89S8252
microcontroller.Can I connect direct the UART serial port of AT89S8252 to the
phone when the power supply of CMOS logic in Siemens C35i is 2.65V and my device has
5V?I know with other CMOS devices I can't make it (Vcc +-0.3V is maximal input
level for a CMOS devices) but on the other hand all data cable with the MAX232
or compatible for this phone uses 5V power supply too.Level for logic is still
compatible when I receive levels from CMOS 3V (or 2.65V) logic to 5V CMOS/TTL
but I'm afraid to send 5V logic to the phone.Typical high level for 5V CMOS is
about Vcc-0.1V and TTL about 3.5V.
I have a "Local Service Organization Service Manual" forSiemens C35i but there's
no limitation in description of the serial data port.
Must I project a level shifter or not?Does anybody know it?Can you help me?

Thanx

Radek