Basic Wireless Communication for Microcontrollers
Chapter 4 - Design Project 3: 900MHz Automatic Error-Correcting Data Link
Interface to the PC
The unit will interface to the PC using a typical RS-232 serial link. A Maxim MAX233 IC is used to do level translation and signal inversion. Since the RS-232 standard is well documented elsewhere, it will not be covered here in this tutorial. We will just note that our RS-232 interface consists of four lines: RX,TX, RTS, CTS. RX and TX are the data in and data out lines, and the interface can operate in full duplex (send and receive at the same time), even though the RF modules cannot do this. RTS and CTS are handshaking lines which are used to control data flow. In other words, if the input buffer in the unit becomes too full, it will signal the PC (by raising the CTS line) to stop sending until the buffer's backlog is reduced. Similarly, the PC can signal the unit (by raising the RTS line) to stop sending.