11

The TOSC switch

The TOSC inputs can be configured as normal I/O pins, or as input pins for a

low-frequency oscillator that can clock the asynchronous timer. The STK503 has

a 32kHz crystal that can be connected to these pins.

The TOSC switch selects what is connected to the TOSC pins on the AVR:

•

Normal port pins - the TOSC pins are connected to the PORTG connector

(set the switch to the position indicated by the text PORTG)

•

32kHz crystal (set the switch to the position nearest the 32kHz crystal)

The External Memory Interface

The AVRs supported by STK503 can access external memories or peripherals

through its External Memory Interface. This interface consist of PORTA

(multiplexed data and address low byte), PORTC (address high byte), and

PORTG[2:0] (RD, WR and ALE).

SRAM footprint

STK503 has a footprint where an SRAM chip can be mounted. The footprint

takes 128Kx8 SOJ and TSOP packages.

Figure 6-1: The SRAM footprint. The arrow shows pin 1.