Set clock input pin for pierce oscillator

Using Arduino Programming Questions
1

Hello everybody,

I was reading about using a silicon oscillator as a pierce oscillator-style clock input here:

I tried hooking up a Attiny85 with a MAX7375AXR805+T as described in the article above which should give me a 8MHz clock and I set the clock to 'External 8MHz' in the arduino ide, however it seems not to work in this way.

I was wondering though, if I need to set the input pin programmatically somehow as the signal is only present on one pin (3) and the other of the two clock pin is set to pinMode(OUTPUT); (pin 2).

Any help is greatly appreciated!

2

Please post a circuit diagram. Hand drawn is preferred, with pins and connections clearly labeled.

To use an external clock source, the CKSEL fuses must be programmed to "00". See the data sheet for the details.

3

Here you go:

schematic
schematic2684×1710 240 KB

I presume setting the clock to "External 8MHz" sets the CKSEL fuses accordingly?

4

I have no idea what you mean by that. I use an ISP programmer to set and check fuses, using ATMEL or Microchip Studio. AVRDUDE can also be used, see for example Setting and reading AtTiny85 fuses – dntruong's Arduino blog

The schematic looks fine, although you should have a bypass cap placed across, and as close as possible to the ATtiny power pins.

5

@jremington : I meant setting the fuse-bits using the menu options in the arduino-ide. you hit it on spot there, though: I checked, and checking the "External 8MHz" option sets the fuses to L:0xFE H:0xDF. In my opinion "External 8MHz" is labelled somewhat ambiguous here, because it refers to "External Crystal Oscillator".
I'll try setting the fuses manually tomorrow and report back...
Thanks for now!

6

The designation "External 8MHz" does not make sense.

If you select fuses for "external clock" then the processor runs at whatever clock frequency happens to be applied, from DC to 20 MHz.

It that frequency is not the one designated by the board you have chosen in the IDE core, settings like the Serial.print baud rate and millis() will be wrong.

7

Hm.. I set the CLKSEL fuses to 00 using avrdude which aparently was successful but now the Attiny seems to be bricked as it is not doing anything at all and it can no longer be programmed using the ISP programmer. Any ideas what might have gone wrong? There actually is a square clock signal from the external clock.. :thinking:

8

Possibly, if you post a schematic showing how you have wired it, and give the details of the external clock signal.

9

Hi,
Have you Googled;

isp programming attiny85 with external oscillator

https://diyodemag.com/projects/programming_the_attiny85

May help.

Tom.. :smiley: :+1: :coffee: :australia:

10

This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.