Is it possible having the Rx and Tx pin of Motorolla’s 68HC11 with two different connections?
January 12, 2010 | In: Motorolla
I’m doing a project involving Motorolla’s 68HC11 microcontroller. In my project, I am required to establish a serial communication (via UART) with a bluetooth module (KC-21 from KCWirefree).
The Tx and Rx pin of M68HC11 have been used for connection with MAX233 (the Tx and Rx pin of M68HC11 is connected to pin RX and Tx of MAX233)
But the Rx and Tx pin of M68HC11 is also needed to connect the Rx and Tx pin of KC-21 bluetooth module.
Can the same pin (Rx and Tx of M68HC11) be connected with MAX233 and KC-21 at once??
For your information, the MAX233 is only used to insert program to the microcontroller. After the program sucessfully inserted, the device is no longer use.
I summon all the experts and geniuses to help me with this matter.
Thank you
2 Responses to Is it possible having the Rx and Tx pin of Motorolla’s 68HC11 with two different connections?
cowboy_in_scrubs
January 12th, 2010 at 2:30 pm
I haven’t done exactly what you are asking, but look at the attached section, and it appears that you can. Read the last part of Section 9.3
Probably the most commonly used aspect of the TxD pin logic is the ability to control
what the pin does after the SCI gives up control. For the pin to revert to a driven high,
write DDRD1 and port D bit 1 to ones. For the pin to revert to high impedance, write a
zero to DDRD1. This high-impedance choice is useful in multidrop systems where
more than one transmitter is connected to a common transmit line but no more than
one transmitter is ever simultaneously using the line. The high-impedance choice can
also be used to make a two-wire SCI system where the TxD and RxD pins of the
M68HC11 are tied together and data travels in only one direction at a time (half duplex).
Since the M68HC11 is a CMOS device, it is a good idea to select the wired-OR option
with DWOM whenever more than one output driver could potentially try to drive the
same line.
Dan Peirce
January 12th, 2010 at 2:57 pm
You need to check the board or the documentation for the 68hc11 board you actually have.
I expect there may be jumpers that you could remove to disconnect the RX pin from the output pin of the MAX233.
You may well be able to download your program using the bluetooth in which case you would no longer need the MAX233 for this project (I am assuming that the bluetooth link can be used as a virtual com link).
I believe the 68hc11 board I used a long time ago had jumpers and a header that allowed one to have direct access to the microcontroller pins.
If the board has no jumpers but the MAX233 is a socketed DIP you could just remove the chip.
The multidrop idea is fine for multiple 68hc11’s connected together as long as only one talks at a time. The Max233 is another story however. That IC has no provision that I can see for being put into a high impedence state.