C Programming for 8051: SFR directions as arguments - c

Question

I'm currently making a very simple Tic-Tac-Toe game with an AT89C51RC2 and I am having issues getting the button input right.
Basically, the input is a 3x3 Button Matrix which I want to utilize by scanning through the rows with a pulse while checking the columns for a connection; pretty basic. However, the way I wanted to do this was by making a unique scroll method that received the row parameter and set it to HIGH accordingly.
I already have
sbit R1 = P1^0;
all through the needed inputs, but I'm not sure if this is correct.
Then, on my main method, I run something like
while(TRUE)
{
scroll(R1);
}
which is named scroll, I have this
void scroll (bit P)
{
P = HIGH; //Sets the row being checked to HIGH (HIGH is already defined as a 1). Same goes with the aformentioned TRUE
...
}
So, this is not working. I know I'm not doing this right, but I had to start somewhere. Is what I am attempting to do possible? Sending a single Pin adress as an overload for a method? If so, what datatype should it be? I was juggling between char and bit but I can't settle.
I hope my question is understandable! If not, I will gladly elaborate and maybe post all the code (although it is quite messy). Thanks, everyone, in advance!

Answer 1

If I understand your question correctly, I could expand your code snippets to look like this:
sbit R1 = P1^0;
sbit R2 = P1^1;
sbit R3 = P1^2;
while(TRUE)
{
scroll(R1);
scroll(R2);
scroll(R3);
}
(Your scroll function remains as is). You are trying to define one function that you can call multiple times, passing in a different pin to assert each time you call the function.
Unfortunately, I am not aware of a way to do exactly what you want to do, because you may not define sbits in a function, either as locals or parameters. I'm sure there's a non-intuitive way to do it in inline assembly with the SETB and CLR instructions (maybe someone else can chime in), but with Keil the C compiler alone it is a no go.
Instead, perhaps you could make a helper function to do the pin assignment. That would let you do something like this:
void setRow(char whichRow, bit whatValue)
{
switch (whichRow)
{
case 1:
R1 = whatValue;
break;
case 2:
R2 = whatValue;
break;
case 3:
R3 = whatValue;
break;
default:
break;
}
}
void scroll (char row)
{
setRow(row, HIGH); //Sets the row being checked to HIGH (HIGH is already defined as a 1). Same goes with the aformentioned TRUE
...
}
And then in your main:
while(TRUE)
{
scroll(1);
scroll(2);
scroll(3);
}
Good luck.

Answer 2

I saw you we're using Keil (really good 8051 compiler IMO). THis compiler gives you a header file for the MCU you are using, which already declares individual bit's of a port to access each of them on Keil page dedicated to Atmel's family of 8051 compiler.
(AT89C51RC2 Keil's webpage http://www.keil.com/dd/chip/3681.htm)
That way, accessing each of the SFR of your chip will be way easier then re-defining them (UART, TIMER, etc).
Usually, a compiler which support's a chip will develop a header file for it's customers.
You can then, after including this header file in your project, access a bit this way :
unsigned char ucBTN = P1_0; //ucBTN equals P1_0 value;
It's, most of the time, the same for every 8051 you'll use, as they use the same "CORE" architecture.