6.8 User RS-232 Interface

The STK600 includes RS-232 hardware that can be used for communication between the target AVR microcontroller in the socket and a PC serial port. STK600 has a 9-pin DSUB connector that can be connected to a PC with a straight serial cable (not a null modem cable).

To use the RS-232 interface, the AVR deviceʼs UART pins must be connected to the appropriate pins on the “RS-232 SPARE” pin header. Use a two-wire cable to connect the AVR deviceʼs RXD and TXD pins to the pin header. The “RS-232 SPARE” pin header is found in the target header section, while the DSUB marked “RS-232” is located on the other end of the card.

Optionally, one can connect the RTS (Request To Send) and CTS (Clear To Send) signals to two free I/O ports. The RTS and CTS signals are used for flow control. The connection is shown below.

If the RTS and CTS lines are not controlled by the AVR device, a jumper shorting the RTS and CTS pins on the “RS-232 SPARE” header can resolve communication problems if the PC side expects these handshake lines to be active.