Serial Port (3.3V CMOS)?

[KansaiRobot]

Hello Everybody.

I would like to ask a question regarding serial ports on a board.
I am reading the specs of one in particular and it says:

CON2 Serial Interface RS232C
CON3 Serial Interface 3.3V CMOS

among others (USB, etc)

Now I know that RS232 is the standard for serial ports but what do they mean by 3.3V CMOS?

I ve never heard a type of serial port named like this. Anyone can enlighten me about this?

Thousand thanks in advance

Kansai

 

[pete_l]

what do they mean by 3.3V CMOS
I am using some CP2102 USB<->serial devices. These run internally at 3.3 Volts and only output signals at 0V and +3.3V not the voltages specified in the RS232 spec. So far as "CMOS" goes, I expect that is meant to imply they won't drive a standard TTL load, just a lower powered CMOS input.

 

[dougy83]

The RS232 serial standard is inverted and has voltages in the range of +/- 25V. The '0' is e.g. +10V and the '1' might be -10V.
The 3V3 CMOS or TTL serial use non-inverted signalling, i.e. a '0' is 0V and a '1' is 3.3V (in the case of 3.3V CMOS).

 

[MikeMl]

Tagging on:

Modern "CMOS" output port pins can source >20mA when high and sink >25mA when low.

TTL ports can only source 400uA when the pin is at 3.5V (even though Vcc=5v), and sink 16mA when low.