Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Atmega8L instead of Atmega8 in USB-ASP

Status
Not open for further replies.

eeeanisur

Newbie level 6
Joined
May 12, 2011
Messages
11
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Location
Rajshahi
Activity points
1,360
Is there any change/problem in USB-ASP Circuit if i use Atmega8L instead of Atmega8.One of my friend has done it with the change of 56R instead of 68R at D+ D-.
 

alexan_e

Administrator
Joined
Mar 16, 2008
Messages
11,895
Helped
2,020
Reputation
4,156
Reaction score
2,031
Trophy points
1,393
Location
Greece
Activity points
64,377
UBBASP uses a 12MHz crystal which can work fine in mega 8 but in mega8L the specification is up to 8MHz so I don't think you can use it.
And the resistor change has nothing to do with different AVR model, maybe it helps in different USB inputs at the pc side.

Alex
 

pranam77

Advanced Member level 5
Joined
Apr 22, 2008
Messages
2,786
Helped
552
Reputation
1,102
Reaction score
370
Trophy points
1,363
Location
INDIA
Activity points
16,411
I have personally used Mega8, Mega8L and Mega8A for my usb-asp circuit and too 100E resistors are used for usb data pins, and i am using it till date without any problems.
Cheers
 

erio

Full Member level 3
Joined
Feb 26, 2008
Messages
176
Helped
27
Reputation
54
Reaction score
23
Trophy points
1,298
Location
Indonesia
Activity points
2,166
i thinks no prolem if you substitute mega8 and mega8L. L mean they can operate to low VCC voltage level, say 2.8 volts
 

alexan_e

Administrator
Joined
Mar 16, 2008
Messages
11,895
Helped
2,020
Reputation
4,156
Reaction score
2,031
Trophy points
1,393
Location
Greece
Activity points
64,377
Why does the datasheet give the grades below if they can both be used for 16MHz? (or 12MHz in this case)

• Operating Voltages
–2.7V - 5.5V (ATmega8L)
–4.5V - 5.5V (ATmega8)

• Speed Grades
–0 - 8MHz (ATmega8L)
–0 - 16MHz (ATmega8)

Alex
 

erio

Full Member level 3
Joined
Feb 26, 2008
Messages
176
Helped
27
Reputation
54
Reaction score
23
Trophy points
1,298
Location
Indonesia
Activity points
2,166
This is just my opinion, but I believe there is absolutely no difference between the two devices. They are *marked* for two different voltage ranges and speed grades so users will limit the clock speed when running at lower voltages, so operation can be guaranteed.
The factory could just as well use one part number, and simply say something like "above 4.5 volts, max speed is 16 mhz, below 4.5 volts, max speed is 8 mhz" or simply follow a voltage/frequency formula. With almost any cmos logic device there is a simple linear relationship between operating voltage and speed performance.

in fact, I have tried "overclocking" this atmega8L. I ran the Igor Cesko USB to RS232 converter like that and I used ATmega8L with 12MHz XTAL and a voltage of 3.3V. All worked fine with that app.
 

alexan_e

Administrator
Joined
Mar 16, 2008
Messages
11,895
Helped
2,020
Reputation
4,156
Reaction score
2,031
Trophy points
1,393
Location
Greece
Activity points
64,377
I'm not sure that it is only about the voltage, a similar example is the mega48/88/168 v series

• Speed grade:
–ATmega48V/88V/168V: 0 - 4MHz @ 1.8V - 5.5V, 0 - 10MHz @ 2.7V - 5.5V
–ATmega48/88/168: 0 - 10MHz @ 2.7V - 5.5V, 0 - 20MHz @ 4.5V - 5.5V

the 2.5v-5.5v is exactly the same but only the second device is specified to be able to work with 20MHz (0 - 20MHz @ 4.5V - 5.5V) .
Maybe in reality they can both work at high frequency but according to the manufacturer you are out of the normal operating speed, I don't know if it a marketing thing or not and maybe it doesn't matter for a hobby circuit but would you use it for a professional design?

Alex
 

erio

Full Member level 3
Joined
Feb 26, 2008
Messages
176
Helped
27
Reputation
54
Reaction score
23
Trophy points
1,298
Location
Indonesia
Activity points
2,166
maybe those rating are for wide operating temperature range (fro -55 up to 125 degree celcius in mega8 datasheet). if mega8L @12 MHz is working on room temperature, there is no guarantee that is working too with, say 80 degree celcius environment.
and yes, "overclocking" is for hobbyist only. on professional design, stay in datasheet boundary. :))
 

santoshaxl

Advanced Member level 2
Joined
Feb 18, 2009
Messages
669
Helped
136
Reputation
272
Reaction score
121
Trophy points
1,323
Location
some where left alone
Activity points
4,899
maybe those rating are for wide operating temperature range (fro -55 up to 125 degree celcius in mega8 datasheet). if mega8L @12 MHz is working on room temperature, there is no guarantee that is working too with, say 80 degree celcius environment.
and yes, "overclocking" is for hobbyist only. on professional design, stay in datasheet boundary. :))
so ok if i want to use atmega8L @12mhz will this work according to datasheet suggest 8mhz maximum
 

erio

Full Member level 3
Joined
Feb 26, 2008
Messages
176
Helped
27
Reputation
54
Reaction score
23
Trophy points
1,298
Location
Indonesia
Activity points
2,166
so ok if i want to use atmega8L @12mhz will this work according to datasheet suggest 8mhz maximum
well, just try it, there is no guarantee that your project will working properly with overclocked microcontroller. BUT i have 2 successfull attemps to overclock microcontroller, once with atmega8L @12MHz 3,3V and once with PIC 16F877 @24Mhz 5V. all is working beautifully.
 

alexan_e

Administrator
Joined
Mar 16, 2008
Messages
11,895
Helped
2,020
Reputation
4,156
Reaction score
2,031
Trophy points
1,393
Location
Greece
Activity points
64,377
A search using google shows many posts that say it works fine.
I guess there is no guarantee because you are out of the specified range (at least from the way that I understand the datasheet) so it depends on how important your application is and the possible "damage" in case that something gets corrupted because I guess that the error would occur as a wrong value or peripheral malfunction.

Alex
 

Status
Not open for further replies.
Toggle Sidebar

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top