68300

>I need some advise on setting up a half-duplex RS485 channel using 
>already set up hardware for both.  My driver chips have both Drive 
>Enable and Receive Enable pins, which I have tied together.  I am 

Oops...see below.


>My question is this:  Is there a status bit or some flagging 
>mechanism I can use to say that when the 68376 is done transmitting a 
>message, I can now safely change the state of the DE/RE bit and 

SCI does: compare and contrast the TC (data has been completely shifted
out) and TDRE (transmit register is empty, ready for next byte) flags.  I
use the TDRE interrupt until the last byte, then switch to TC.  

As far as I know, the 'G' mask TPU UART does not have a TC flag, only TDRE.
 Maybe someone can offer a link to some custom TPU code to add the TC flag...


>I am hoping to avoid having to use any kind of delay timer to switch 
>from TX->RX or RX->TX.

I've also done the trick where you tie the receiver and transmitter
together, transmit the last byte, wait for the last byte to come in the
receiver, and then disable the transmitter.  However, you must leave the
receiver enabled during transmission, so tying the 485 DE and /RE lines
together won't work!


newell