hi i am a beginner in the embedded systems.....please help

in the I/O ports section i have read.....
TRIS register means that it will define the direction of the pin which is connected to the particular port
exmple:

TRISGbits.TRISG1 = 1 will make that line in the input mode...

but what does
PORTGbits.PORTG1 = 1;
and
LATGbits.LAT1 = 1;

means??

does it mean that it would write 1 to the corresponding line??

thanks
Puneet Gupta

 

What programming language and compiler are you using?

 

As you have surmised PORTGbits.PORTG1 = 1; writes a 1 to port G bit/pin 1 and
LATGbits.LAT1 = 1; writes a 1 to latch G bit 1.

In the case of writing, the two instructions are interchangeable but if you were doing a read then there can be significant differences between reading a port (pin) and reading the contents of the port data latch.

 

The rule of thumb is to write to the LAT register and read from the PORT register to avoid read-modify-write problems of writing directly to the PORT. Check out section 12.2.2 of the PIC24F family reference manual for the details.

 

houta69;

I think you have it the wrong way around.

To quote from the ref manual section 12.2.3

The differences between the PORTx and LATx registers can be summarized as follows:
• A write to the PORTx register writes the data value to the port latch.
• A write to the LATx register writes the data value to the port latch.
• A read of the PORTx register reads the data value on the I/O pin.
• A read of the LATx register reads the data value held in the port latch

To prevent the read, modify, write problem you read from the latch and write where-ever you like since when you write to the port you are actually writing to the latch.

 

Greetings AlexR -

This subject comes up at least once a month on the MCP forums. Here's a recent example.

There's also a wiki link embedded in that thread that covers the topic.