10Mhz vs. 20Mhz

Hello,

So the bottom line is that we cannot find the 20Mhz Atmega 168 chip. However, we did find the 10Mhz of the same model.

Can anyone please tell us if this would cause us a problem?

Your feedback is MUCH APPRECIATED.

Cheers,
Mahdi

you would have to recompile all the firmware for the new F_CPU, updating baud registers and any other timing-dependent code. you may also have to print slower. Also, the 168 is apparently too small for a lot of the recent firmware so you may have to be careful with versions too.

Hey, thanks for the reply.

You mentioned that the chip is too small and might not be compatible with the recent firmware.

Is there anywhere else on the website that confirms this?

Are you sure about it?

So why would RepRap produce firmware that is not compatible with the chip they've recommended.

If all this is true. What is an alternative?

Thanks for you help,
Mahdi

latest motherboard uses atmega644p ala sanguino

[www.reprap.org]
[reprap.org]

Some of the firmware is based on interrupt driven routines for the stepper motor and they use the code path length for timming on driving the step pulse. Though a slower processor might mean a longer step pulse.

Sound like you are putting together your own electronics. The atmega644p is a dual serial port version of the chip and might not be readly avaialble. It is used with the idea of using the second serial link to talk to slave processors on different types of extruders.

The basic atmega644 only has one serial port and is more readly available.

The atmega 168 is really tight on memory for current versions of the firmware. So using a atmega644 will give you more ram and more pins.

All of the AVR chips have a internal 8mhz oscillator, AFIK a 644 at 8mhz might be a viable option to explore.

There was discussion of using a basic atmega644 here:

[dev.forums.reprap.org]

and

[dev.forums.reprap.org]

Hey,

thanks a lot for the great reply.

But just to clarify, the chip suggested on the reprap parst lister for the
extruder is an atmega168 (http://parts.reprap.org/part/module/Extruder+Controller+v2.2)

So, this is the circuit that I'm talking about: the extruded not the motherboard. We've already got an atrmga644 for the mother board (as suggested by theb parts lister).

Our problem is the chip (atmega168) for the extruded (not the motherboard).

However, are you suggesting that we can also use an atmega644 for the extruded as well. So basically, the 644 is just an enhanced version of the 168?

If yes, will this cause us configuration problems with the circuit? (we're getting the PCB from MakerBot)

You seem to know these stuff very well, and I'm quite interested myself. Your feed back will be of great help to me.

Thanks,
Mahdi

644 is an enhanced version of the 168, however it probably has more pins and a different pin-out, so can't just drop it into the board.

now that I think about it, your 10MHz '168 will probably run fine at 16MHz.. atmel chips overclock very nicely as long as you don't run them close to their voltage limits, and afaik the extruder gives it a healthy 5v (lower limit is 2.7v iirc)

if it blows up, don't blame me though - better off recompiling the firmware for your lower F_CPU

Obvously if you are using the extruder controller PCB from makerbot then you should stick with the 168 for pinout compatibility.

The extruder controller has a lot less multitasking to do so running it at 8 or 10mhz should be minimal impact. Again with a NonStandard clock rate you have to recompile the boot strap and the base Audino enviorment.

Also if using the internal clock the fuzes that you set will be different. I think from a design standpoint it has a 16mhz clock to be compatible with the reference standard arduino board.

I tried running a 10mhz 644p at 16mhz and it did not work.

Edited 2 time(s). Last edit at 11/28/2009 06:45PM by freds.