Yes, Modbus requires ~4 characters of idle time between frames. When I mean ilde byte, I meant the UART will send out a 1 as the start bit. So what I really want is the xmit line to remain at idle condition (logic 1) for 4 character times. Problem with using a simple delay is that would require the use of a free timer. I'm trying to get away from doing that. On the Motorola HC11, I can use the ILIE (supplied by the UART) and the UART would give me the TI interrupt even though it's not sending anything out. ie, xmit line remains idle. The whole point of this is I want to get x number of UART character time delay without using an extra timer of the 8051 and without messing with the xmit line of the UART. Is this possible?

Thanks
Andy

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It would be possible to use the "hard" UART for actual data and a (partial) soft UART just for the idle bytes (BTW How do you keep the receiver from seing a bit of an idle byte as a start bit). I do not know squat about Modbus, but is "idle bytes" anything but a gap in transmission of a given length (multiple of 1/baud value?), if that is the case a simple delay will take care of it.

Erik