STK504 Clock Sources

The STK504 can supply three kinds of external clock sources to the AVR

mounted in the ZIF socket: On-board 32kHz crystal, a higher frequency crystal

mounted in the on-board socket and a clock supplied from STK500.

The clock switch

The clock switch has three positions, EXT, LF and HF as shown in figure 5-1.

See table 5-1 for function.

Table 5-1: Clock switch positions

Position

Function

EXT

Clock from STK500. (See STK500

documentation for more information.)

LF

On-board 32kHz crystal

HF

Crystal placed in the socket marked HF

on STK504

Figure 5-1: Clock switch

EXT – STK500 as clock source

If you put the switch in the EXT position, you will supply the externally generated

clock (from STK500) to the XTAL/TOSC pins of the AVR. Check the STK500

help file for more information on how to set the different clock options.

LF – Low-Frequency 32kHz crystal

The STK504 has a 32kHz (32,768Hz) crystal that can be connected to the

XTAL/TOSC pins when the switch is set to the LF position.

HF – High-Frequency crystal

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