Atmel STK594 Tosc Switch, Universal Asynchronous Receiver Transmitter Uart, Second RS-232C Port

Using the STK594 Top Module

2.5TOSC Switch

The AT94K device provides dedicated I/O pins for TOSC1 and TOSC2, rather than sharing with the general purpose I/O pins. The TOSC switch selects whether or not the 32 kHz crystal is connected to the pins of the device.

Figure 2-5 shows a simplified block schematic on how this is implemented.

Figure 2-5.TOSC Block Schematic

FPSLIC

TOSC2

TOSC1

32 kHz

TOSC

Switch

2.6Universal Asynchronous Receiver Transmitter (UART)

2.6.1Second RS-232C Port

Unlike traditional AVR microcontrollers, the AT94K device provides the option of having separate I/O pins for the UARTs rather than sharing with the general purpose I/O pins.

Figure 2-6 shows the pinout of a header for the dedicated UART pins.

Figure 2-6. UART Header

1 2

RX0 TX0

RX1 TX1

UART

The AT94K device has an additional UART. The RS-232 port on the STK594 board has in addition to the RXD and TXD lines support for RTS and CTS flow control. Figure 2-7 shows a simplified block schematic on how this is implemented.

Note: The UART in AT94K devices does not support hardware RTS or CTS control. If such functionality is needed, it must be implemented in software.

Figure 2-7.UART Block Schematic

RS232 SPARE2

4

6

2

3

7

8

5

RS-232/Logic Level

Converter

RxD	TxD
CTS	RTS

This UART can also be used from devices placed in the STK500 board. Simply connect the appropriate port pins to RXD and TXD on the STK594 board.

Note: If no software RTS/CTS flow control is implemented, a jumper shorting RTS and CTS will ensure correct communication with an external application that uses such flow control.

2-4

FPSLIC STK594 User Guide

2819A–FPSLI–07/02