Initializing Ports on MicroController

[theone_in_themoon]

Hi

Im using ATMEL 89C2051 uC. I have used it before but i have come up with a unique problem.

i.e. When i need to communicate serially with PC through RS-232... it requires that i do NOT initialize the ports with 0x00. [Initializing with 0xFF works somtimes].

However if i do not initialize the ports (so that i can do serial comm.) then the uC does not read the value at the pins [By sbit ].

Its either the serial communication OR Reading Pin values ........... but i need to have both these tasks performed.

Can anyone suggest or guide me with wat might i be doing wrong ???

Thankyou

P.S. Please Do reply ... i really need help

 

[XNOX_Rambo]

Some instructions read the port latch and some read the port pin.

Study section 4 of this datasheet carefully to understand the difference:
**broken link removed**

/Rambo

 

[theone_in_themoon]

Im using a C51 compiler. So that means im NOT using assembly language instruction set. Im using normal C language.

 

[XNOX_Rambo]

Well, then maybe this will be of use: https://www.keil.com/support/docs/2071.htm

 

[glenjoy]

Initializing ports with 0x00 means you are making them as an output port, therefore you will not be able to receive data from your UART.

I am quite confused in your question on reading the UART and reading the ports, if you declare the two pins as the for the UART and I believe they are built to have that function as a substitute for being an I/O pin.

The UART function is done automatically by your microcontroller but of course you must initialize the ports properly before making the I/O pins do a certain job.

At initialization, all pins of microcontrollers are expected to act as an input port, initializing the UARTs could have internally controlled the RX pin of the micro to act as an output.