Help understanding UzeBox

[!LH@N]

Hi everybody!
I am an engineering major and thought that Uzebox would be an awesome way to get a better understanding of electronics and start it as a hobby. So I have decided to build everything by myself and try to understand as much as I can on the go. So I have been looking at the schematics and have a few questions.

1)What is A/V on the Schematic? What is it for? I connect lines RED, GREEN and BLUE from the DAC to the AD725 and also to A/V. Why is that?
2)What is EXT?
3)What is ISP?
4)As far as I understood, SD/MMC is the memory card slot. Why is it connected to ISP and to the RESET-Pin of the ATMega?
5)The MCP1700 is there to regulate the Voltage down to 3.3V, but it looks like it is not connected to the ATMega at all. What is it for? As far as I can see, the ATMega is running on 5V?
6)I read that the DAC is supposed to be an R/2R-DAC. But the schematic doesn't look like it. Why is that?

Thanks for the answers!
Ilhan

[uze6666]

Hi,

1)What is A/V on the Schematic? What is it for? I connect lines RED, GREEN and BLUE from the DAC to the AD725 and also to A/V. Why is that?

This is because those signals also go to the external header. This header can be used for external RGB things like a JAMMA arcade cabinet.

2)What is EXT?

This the second external header that exposes sharable pins and all unused pins of the ATmega644.

3)What is ISP?

ISP stands for "In system programming". It's the port & protocol used to program the '644.

4)As far as I understood, SD/MMC is the memory card slot. Why is it connected to ISP and to the RESET-Pin of the ATMega?

The ISP port uses the SPI protocol (serial peripheral interface). This is a standard communication protocol that is supported by the SD/MMC controller. It also has a reset, so both the SD and '644 are reset at the same time.

5)The MCP1700 is there to regulate the Voltage down to 3.3V, but it looks like it is not connected to the ATMega at all. What is it for? As far as I can see, the ATMega is running on 5V?

It is used by the SD card.

6)I read that the DAC is supposed to be an R/2R-DAC. But the schematic doesn't look like it. Why is that?

It was originally a R2R in the very first schematic release. Later it was updated with a weighted DAC, which uses less resistors and works equally well.

Hope that helps,

-Uze

[!LH@N]

Hola!
Thanks for the kind reply!