Urgent

[YAN-1]

Hello. I intend to buy a GPS device that interfaces through an RS232 port and that contains two full duplex serial ports that operate at CMOS (3.3V) voltage levels. I need to interface this GPS module with a 16F877 through the UART module but I have no idea about whether the signal levels of the UART module of the PIC are 5V or 3.3V or whether I can interface it in the first place. Will I need a voltage level conversion chip like a MAX?

Please help as soon as you can as time is critical.

Thanks a lot.

Nichola

 

[Oznog]

Helpful hint- under "topic", try putting in the topic of your question.

The PIC will output whatever your Vdd is. If it's 5v it will put out 5v. That may or may not be acceptable to a 3.3v GPS, if you're lucky they designed an input stage that will not be harmed by 5v. Otherwise you may need to use one of a number of tricks to lower the output voltage, or get a low voltage PIC that can operate on 3.3v. The GPS's spec sheet is the ONLY way to determine if it can take 5v. If it is in doubt, you will need to lower the output voltage to 3.3v.

The input voltage that the PIC will interpret as a 1- and that applies to the UART just like any other input- will be given on your spec sheet under "electrical characteristics". 3.3v is usually within spec for a "high" for input pins which are not schmitt-triggered, and a level converter will not be needed.

GPS usually uses NMEA protocol in case you don't know.

 

[yo5oqa]

I have a Lassen SQ GPS module, at 3.3V, and I connect it very simple to PIC16f877:
- PIC RX to GPS TX;
- PIC TX to GPS RX through an 100 ohm resistor and a 3.3V Zenner to ground;
I had used hardware Usart from Pic and works very well.