In my design I have a free 8051's port-1. It's a bit-addressable ll'l port. I have a iPAQ HHT with serial interface. But my TxD and RxD of 8051 (UART) are used for prog and debugging. How can I interface my iPAQ?
There are several options of connecting more than one device to a 8051-derivative via serial port ..
First option is purely software solution and creation second UART in software ..
Here is one example of software UART: **broken link removed**
Second option is a hardware soulution: if the Rx and Tx pins are already used for programming and debugging you can add a couple of AND gates and one pin from Port1 to switch between two inputs and two outputs ..
In this way the same (and only one) UART will be used to operate with two external devices ..