Hi Panos,

I saw your question and thought I'd add my two cents on this.
    I have two questions concerning the 8051 microcontroller and its serial
port.

    ==>  Have you seen my book "Programming and Customizing the 8051"?  It
has a lot
    ==>  of the information that you are looking for here.

    ==>  Are you aware of the Philips 8051 List Server?  It is devoted to
the 8051 with
    ==>  lots of knowledgeable people who can help you out.

    ==>  You can get links to both at my web page:
    ==>  http://www.myke.com

    ==>  Question 1.  Yes you can and as people have noted, you can do that
with the
    ==>  Standard Serial Port - although I would use the RS-485 transceiver
to do this function
    ==>  instead of tying the TX and RX lines together at the 8051.

    ==>  Have you seen Jan Axelson's "Serial Port Complete"?  It is an
excellent reference
    ==>  on serial communications (with a lot of information on RS-485).  I
have links to it
    ==>  from my web page (from the "Book Room") as well.

    ==>  Question 2.  If you have an 8051, why don't you use one of the I/O
ports with the
    ==>  Parallel Port's "_Strobe" line connected to one of the interrupt
input lines?  By
    ==>  doing it this way, you really don't need any buffers (unless of
course you don't
    ==>  have the I/O lines available for it).

    ==>  I don't know of a good reference (that is available yet...) that
discusses this.


    ==>  myke

    ==>  PS. Sorry I've been so quiet - *lots* going on around here.  I'll
comment on the
    ==>  servo notes tonight.


    Question No1.

    I wonder if there is a way i can convert the serial port of a 80C51 into
a serial port with CSMA/CD (Carrier Sense Multiple Access with Collision
Detection). I don't mind using any external circuitry or 8051 port pins as
long as i use the serial port of the 8051 and not a networking peripheral.
Note that the serial comunication will not be using a baud speed of more
than 19200. Plus i will be interfacing the serial port to a RS-485 or RS-422
transceiver and not RS-232 due to the long distances between every node.

    Question No2.

    Is there a way i can connect the 8051 with the parallel port of a PC ? I
think i must use a 74HCT543 latching transceiver. The bus connection must be
bi-directional. However i need to be able to control one or two more pins
from the parallel port for interrupt request (pin no1) and discrimination of
address/data/command (pin no1 or even pin no1 and no2). Note that the
parallel port will be connected to a 8051 based system that will be used as
the primary server for an RS-485 network of many 8051 based systems.
    Is there a site where i can find some serious information on the PC
parallel port (pdfs) ??


    P.S. There is no need to answer to both questions.

    Thank you in advance for any help...

    Panos Kenterlis
    Technological and Educational Institute of Piraeus
    Athens - Greece