Well gentlemen, I have found your replys useful and informative. I have
worked for many years with RS485 using 75176 and max485. I would like to
add that it is almost always possible to receive 485 on a PC by just using
GND and one side of your 75176 output to rec. Most PC do not really support
the RS232 spec. and will work just find with 0-5 volt signals. To turn your PC
RS232 into RS485 is harder but not that hard. Eric your coment on the TI
Interrupt is right on and you have no idea how long I worked on that problem.
Timing of communications is a big problem. I have found that is always a good
idea to place a delay before any respond to a received transmission. This applies
to both the PC and the target board. You also should delay at the end of each transmission a small amount to allow for the TI problem. One more idea for you. I have tied both
DE and RE together on one port pin many time and this works just find. But I
like to use two port pins if possible, one for DE and one for RE, This way it is very simple to built in a test routine to check the condition of the 75176. You just send out and the echo comes back if you receive it your 75176 is good. The test
should be run when not hooked to your com lines.