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RS-232 Driver

The STK503 has an RS-232 driver operating at target voltages from 1.8 to 5.5V

with a maximum speed of 480kbps. There are two transmit and two receive pins.

With the RS-232 port available on STK500, you have three channels available for

your design.

The driver pins are available on the connector in the lower right corner of the

STK503 (see figure 7-1 and 7-2).

Figure 7-1: The RS-232 connector

To use the driver you must connect the logic level pins to the AVR and the RS-

232 pins to the external device. The connector is marked with AVR and RS-232,

where the pins on the AVR side must be connected to the RxD and TxD pins on

the AVR, and RS-232 side connects to a connector or your RS-232-enabled

device. The arrows show the signal directions.

Figure 7-2: RS-232 connection

As the STK503 has no 9-pin or 25-pin connector, you must make your own

connection. You can however decide if you will use only TxD/RxD lines, giving

you two channels, or if handshake signals like RTS/CTS or DTR/DSR will be

used. In the latter case, you must connect the handshake signals to regular

PORT pins that are controlled by software.