Yes, scope pics are with connected HU (Pioneer AVIC-D2).
What do you mean by upload firmware with diagnostics on?  The firmware was already uploaded.
Thanks.

Okay, I am now revisiting this project 10-months later!
Unfortunately, I was never able to get it to work.  I am almost certain the circuitry is assembled correctly, but I'm not sure.  I tried to diagnose the problem by myself, but I am lacking in any real electronics knowledge.

I took some measurements of various test points on my circuit with a scope, would somebody please take a look and tell me if anything looks wrong?

This is the schematic of my interface showing the test point locations.
TP1 - Atmega8 Pin 14
TP2 - 2SA733 Base
TP3 - 2SA733 Collector
TP4 - LM339 Pin 3
TP5 - LM339 Pin 1

IP Bus TTL signal I measured on an HA12240FP inside a CD-IB100

Link to the pics above

Any help will be greatly appreciated!

Ok, I see YAPP.  I can't use YAPP since it doesn't support Atmel Dragon.
I found a handy fuse calculator here:
Fuse Calculator

I think I have the fuses set correctly, 0x2F & 0xC9.
Still no communication though.  I must have a hardware problem somewhere. 

Sorry, I did find the image earlier and forgot to update my post, but those fuse settings don't seem to work and they kill the ISP.
Maybe I didn't translate them correctly?  I am using AVRStudio4 and the fuse settings look a little different.  What program did that screenshot come from?
You have CKSEL0, CKSEL1, CKSEL2, CKSEL3 = unchecked.  Is that same as CKSEL=[0000]?  SUT0 = checked, SUT1 = unchecked, is that same as SUT=[10]?  BOOTRST=unchecked, is that same as BOOTRST=0 or BOOTRST=1?  I think AVRStudio4 BOOTRST checked is same as BOOTRST=0.

Maybe it would be easier if I just use the same program as you used, but my programmer is an Atmel Dragon so the program I use must support it.

Can you tell me the hex values of the fuse bytes?

Yeah, Mega8 has fuse bits or option bits.  I know the one needs to be set for external oscillator, but I don't know what to do about the rest.  I wonder if that's why my HU doesn't recognize M-CD?

Thanks Vitat, I have fixed the schematic and built the circuit.
Will your firmware do anything if Yampp3 is not connected?
I tried connecting to my stereo's IP-bus, but M-CD is not available.  I am just trying to test it right now.
Also, what are the correct settings for the Fuse bits?

Thanks Vitat, I have fixed it, I think!

Does the attached schematic look correct if I want to convert between IP Bus and 5V Serial?
I will use an external circuit to convert 5V serial to RS-232 so that part isn't in the schematic.

Ok, I think I understand.  I looked at schematic and see RX and TX connected to INT0 and ICP.
I was trying to learn by reading C source, but I don't know C so I misunderstood it for using the UART.
Thanks for the logging firmware!

Is Atmega64 compatible with Atmega8 firmware?

I am a little confused.  How come the Atmega8 UART can be programmed to talk to the CAN-BUS IC, but an RS232 port cannot, not even through MAX232?  I thought RS232 uses a UART too?

Is any extra circuitry required to connect converter between head unit and another device?  Or can it just be connected in parallel like a Y-splitter?

Is a logging firmware already available, or would I need to modify your Yammp3 firmware to turn it into a logging firmware?  I did a search and found no references to logging firmware.  Unfortunately, I am unfamiliar with the C language.

Hi, I also want to connect IP-Bus to computer.
Is the only thing necessary, is to connect CAN-BUS IC to MAX232, then connect MAX232 to serial port?
If yes, then what settings are necessary (baud rate, bits, parity)?

Is it possible to connect a converter to the IP-Bus when there is already another device on it?
My goal is to use the converter to "listen" to the IP-Bus and log all communication on it.  I want to decode the XM Radio mode.

Also, before I start, has the XM Radio mode already been decoded?