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
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
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.
FPSLIC STK594 User Guide