[SOLVED] Set Low Fuse Bit, Now Can't Program over ISP

Don't you need to connect the LED+resistor between the pin and ground, and then between the pin and Vcc, and check it lights in both cases? I wouldn't like to guess what state the CKOUT pin will have when there is no clock.

I don't think there is any danger of damaging the resonator if you leave it in place. However, the resonator will present quite a low impedance at frequencies that are not very close to its resonant frequency, and the signal from XTAL2 will provide negative feedback via the resonator to XTAL1. So it may be difficult to provide enough drive from the clock source, unless you match the resonator frequency. I guess it's worth trying with the resonator connected first.

Aakash:
@Nick - Should I go lower than -B5 rate?

-B5?

I set mine to run at 128 KHz and could reprogram it with -B250. So, no.

@dc42 - I have Saleae Logic analyzer, should I be able to use that to test if there is a signal being outputted?

I don't think that's relevant.

Have you reprogrammed the high fuse by any chance?

Aakash:
@Coding Badley - the system runs at 3.3V, when selecting the current limiting resistor should I account for that voltage or a lower one?

3.3V.

dc42:

[quote author=Coding Badly link=topic=132832.msg999568#msg999568 date=1353141095]Connect an LED + current limiting resistor. If the LED lights, the resonator is running. If the resonator is running, you can reprogram the processor; it's just a matter of getting the ISP bitrate low enough.

Don't you need to connect the LED+resistor between the pin and ground, and then between the pin and Vcc, and check it lights in both cases? I wouldn't like to guess what state the CKOUT pin will have when there is no clock.[/quote]

Ooh. Good point. LED needs to light both ways around to ensure the clock is running.

[quote author=Coding Badly link=topic=132832.msg999568#msg999568 date=1353141095]@dc42: Does the resonator have to be removed? Will it be damaged by a clock signal on XTAL1?

I don't think there is any danger of damaging the resonator if you leave it in place. However, the resonator will present quite a low impedance at frequencies that are not very close to its resonant frequency, and the signal from XTAL2 will provide negative feedback via the resonator to XTAL1. So it may be difficult to provide enough drive from the clock source, unless you match the resonator frequency. I guess it's worth trying with the resonator connected first.[/quote]

Is a series resistor between the clock source and XTAL1 pin necessary? A good idea?

Aakash:
@dc42 - I have Saleae Logic analyzer, should I be able to use that to test if there is a signal being outputted?

I'm not familiar with that device, but if you connect one of the channels to the CKOUT pin, then it should give you a frequency readout for that channel if there is a clock signal there.

As I've very little idea what sort of impedance the resonator will present, I would use one for safety, but only 100 ohms or so.

Nick,

I tried using -B250:

avrdude -p m328p -c avrispmkii -P usb -B250 -F

avrdude: stk500v2_command(): command failed
avrdude: stk500v2_program_enable(): bad AVRISPmkII connection status: Unknown status 0x00
avrdude: initialization failed, rc=-1
avrdude: AVR device initialized and ready to accept instructions
avrdude: Device signature = 0x000000
avrdude: Yikes!  Invalid device signature.
avrdude: Expected signature for ATMEGA328P is 1E 95 0F

And regarding the high fuse question, I'm pretty sure. All I did was read in the fuse bits from the fresh chip and change the low bit by hand in AVR Studio. Though, I always could be mistaken.

@dc42 - I don't think CKOUT is outputting anything (see attached screenshot)

You won't measure an 8 MHz signal at an 8 MHz sampling rate.

Aakash:
@dc42 - I don't think CKOUT is outputting anything (see attached screenshot)

I think you're right, although you'll need to use a sampling frequency much greater than 8MHz to reliably see a 8MHz signal, so check with it set to 24MHz.

If you have an Arduino, you can use it to generate a clock signal to feed to XTAL1. Don't forget to use a potential divider to drop the voltage if it is a 5V Arduino.

PS - is it a 3-terminal resonator? If yes, have you grounded the centre pin? If no, are you certain that the capacitors you connected between the XTAL pins and ground are about the right value, and you haven't accidentally used a value that is much too large?

@dc42

I think the output looks the same at 24MHz. I have a 3.3V Arduino, what freq signal should I be generating to feed to XTAL1? Also, should I still try connecting XTAL1 and CKOUT?

And regarding your resonator question: It is a three terminal resonator. I didn't use my own caps as I believe they're built in. http://www.digikey.com/product-detail/en/CSTCE8M00G55-R0/490-1195-1-ND/584632

Thanks,
Aakash

EDIT: And yes, the center terminal is grounded.

The datasheet says that resonator has internal caps. I've use 8MHz ceramic resonators in my designs with no problems, although not at 3.3V and I set the low fuse byte to a more appropriate value.

Try feeding a clock signal from your 3.3V Arduino to XTAL1 through a 100 ohm resistor. The frequency doesn't matter much, I would try around 1MHz in the first instance. Leave CKOUT connected to your logic analyser so that you can check that you have a signal there.

Here's a sketch I use to get bursts of a known frequency on the OCR1A pin (pin 9 on an Arduino Uno):

// Generate a square wave of a given frequency on the OCR1A pin

#define REQUIRED_FREQUENCY  (38000)
#define REQUIRED_DIVISOR ((F_CPU/REQUIRED_FREQUENCY)/2)

#if (REQUIRED_DIVISOR < 65536)
# define PRESCALER  (1)
# define PRESCALER_BITS  (1)
#elif (REQUIRED_DIVISOR < 8 * 65536)
# define PRESCALER  (8)
# define PRESCALER_BITS  (2)
#elif (REQUIRED_DIVISOR < 64 * 65536)
# define PRESCALER  (8)
# define PRESCALER_BITS  (3)
#elif (REQUIRED_DIVISOR < 256 * 65536)
# define PRESCALER  (8)
# define PRESCALER_BITS  (4)
#elif (REQUIRED_DIVISOR < 1024 * 65536)
# define PRESCALER  (8)
# define PRESCALER_BITS  (5)
#else
# error Bad frequency
#endif

# define TOP        (((REQUIRED_DIVISOR + (PRESCALER/2))/PRESCALER) - 1)

void setup()
{
  pinMode(9, OUTPUT);
  digitalWrite(9, LOW);
  TCCR1A = 0;
  TCCR1B = (1 << WGM12) | PRESCALER_BITS;    // turn on
  TCCR1C = 0;
  OCR1AH = (TOP >> 8);
  OCR1AL = (TOP & 0xFF);
}

void on()
{
  TCNT1H = 0;
  TCNT1L = 0;  
  TCCR1A = (1 << COM1A0);
}

void off()
{
  TCCR1A = 0;
}

void loop()
{
  // Generate a burst 2ms long, then wait 10ms before generating the next one
  on();
  delay(2);  
  off();
  delay(10);
}

PS - have you checked for solder bridges on the XTAL1 or XTAL2 pins of the mcu?

@dc42 Thanks for the suggestion. I'll check for bridging tomorrow. I'll have to order a 100ohm resistor to test out the clock signal feeding. So that'll take a few days. I'll reply back with results then.

Thanks again everyone.

If you haven't got 100 ohms, try with 1K or whatever value >100 ohms you do have - it might work.

[EDIT: the datasheet for that resonator very helpfully gives the impedance at various frequencies. Based on that, at a clock frequency of 1MHz, even a 10K resistor may not be too high a value for it to work.]

@dc42 - I attached various screenshots of logic analyzer outputs. The file names are as follows:

  • RAW_SOURCE: the output of connecting the analyzer directly to Pin 9 of the clock source Arduino, which is running your code, through a 1.5K resistor.
  • XTAL1: The analyzer output on CKOUT due to connecting Pin 9 of source Arduino to XTAL1 pin on m328p through a 1.5K resistor
  • XTAL2: The analyzer output on CKOUT due to connecting Pin 9 of source Arduino to XTAL2 pin on m328p through a 1.5K resistor

I connected both the Arduino, m328p, and the logic analyzer to a common ground throughout these tests.

How should I proceed?

Thanks again!
Aakash

Try running my "chip detector" sketch:

That generates a clock signal on pin 9 as well in case you need it.

Nick,

I installed your sketch and hooked up the ICSP lines and the only serial output I got was "Atmega chip detector." I also tried connecting D9 to XTAL1 through a 1.5K resistor and the same was outputted.

Should I be doing something differently?

Thanks,
Aakash

I wouldn't worry about the resistor, but that sounds OK, assuming you followed my wiring. Sounds to me confirmation that it isn't responding to programming.

I wonder if, when you were changing the fuse in the Atmel Studio, you accidentally didn't notice that at the same time the high fuse was set to something that wasn't appropriate (like SPIEN). Once you turn off SPIEN you can't program through the SPI interface.

Nick,

AVR Studio read in the existing fuses, and showed me that only the low fuse had been modified (the field shows up with a notice once you modify it)

So, I'm pretty confident that I didn't change anything except low fuse.

Thanks though.
Aakash