GPS 3.3V & 5V Atmel UART

Tips and questions relating to the GPS modules from SFE
Posts: 1
Joined: Sat Nov 04, 2006 10:02 pm

GPS 3.3V & 5V Atmel UART

Post by Chute » Sat Nov 04, 2006 10:10 pm

I would like to know simple effective solutions to connecting a 3.3V GPS serial port TTL level signaling to a 5V Atmel UART.

My questions include:
Most 3.3 chips are not 5V input tolerant. Right?

Will a 3.3V TTL level GPS chip exceed the Vih threshold on at 5V Atmel UART?

How can I make this easy without resorting to using Max232 like chips and changing from 3.3VTTL level to true RS232 and back to 5V TTL level UART?

I want to be able to both transmit and receive from the Atmel to the GPS (both chips adjacent on the board).

Thanks for any advice,

Posts: 480
Joined: Wed Mar 29, 2006 12:12 pm

Post by seulater » Mon Nov 06, 2006 5:47 am

your ATMEL UART is 0v/5v levels, not true RS232 levels.
so the 3.3v transmit pin from your GPS to the 5v ATMEL RX pin is fine.
the problem will be your 5v ATMEL TX pin to the 3.3v GPS RX pin.
but a simple resistor divider will take care of this problem for you.
just make your resistor divider so that 5v in will be 3.3V out and then take that output to the GPS unit and you done.


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