Assigning pin status

"in the datasheet it says..."

Standard 'C' has no way of dealing with individual bits in a byte - so that has to be a compiler-specific extension.
What compiler is the datasheet referring to?

For Keil C51, you have to define "P0_DIR" as an sfr, and then define bit 1 within that SFR as an sbit.

Or you can define the sbit directly.

sfr and sbit are Keil-specific language extensions - look them up in the C51 Manual.

"in the datasheet it says..."

Standard 'C' has no way of dealing with individual bits in a byte - so that has to be a compiler-specific extension.
What compiler is the datasheet referring to?

For Keil C51, you have to define "P0_DIR" as an sfr, and then define bit 1 within that SFR as an sbit.

Or you can define the sbit directly.

sfr and sbit are Keil-specific language extensions - look them up in the C51 Manual.

or take a look at Keil's header file for this device:

http://www.keil.com/dd/chip/3605.htm

I found this in an example, but cant understand how it is doing what it says its doing??

P0_DIR |= 0x02; // P0.1 (RxD) is input

Leigh

"cant understand how it is doing what it says its doing??"

Which bit don't you understand - the 'C' syntax, or the comment.

The 'C' syntax is setting bit-1 in P0_DIR - but your original post was, apparently trying to clear that bit.

Whether clearing that bit in that register does actually set P0.1 (RxD) to be an input is something you'll have to check in the Datasheet.

Comments can, of course, be wrong...

Its the 'c' syntax, how is it that 0x02 is known to be setting P0.1?

0x01 = 1<<0 = 1 = bit 0 (least significant bit)
0x02 = 1<<1 = 2 = bit 1
0x04 = 1<<2 = 4 = bit 2
0x08 = 1<<3 = 8 = bit 3
0x10 = 1<<4 = 16 = bit 4
0x20 = 1<<5 = 32 = bit 5
0x40 = 1<<6 = 64 = bit 6
0x80 = 1<<7 = 128 = bit 7 (most significant bit)

ahh ok, i see, well i what i want to do is to set P0.5 as an input and to only transmit when a pulse is received on that pin, i have set pulse_pin (p0.5) as an input using the above, along with p0.1 for other reasons.

i.e. P0_DIR = 0x22;

in init() function i have set pulse_pin = 0 then the code for main() is as follows:

if (pulse_pin = 1)
{ transmitter()
}

is this the correct way of 'asking' if a pulse is received, i.e. goes high from a voltage.

thanks again

P0_DIR |= 0x02; // P0.1 (RxD) is input

"how is it that 0x02 is known to be setting P0.1?"

It isn't!

It's setting P0_DIR.1 - which, if the comment is to be believed, configures P0.1 to be an input

"i have set pulse_pin (p0.5) as an input ... i have set pulse_pin = 0"

What happens on this chip when you write to an input pin?!