Thanks,  Let me explain what I want to do first.
I need to connect AX-12 servo to one TTL UART port. 
Is UART-0, UART-1 TTL level or 3.3V?
AX-12 servo takes full duplix signal.  Where can I get the cireuit to merge TxD and RxD line?
Yes,  I am thinking of trying the roboaudio by itself. can you tell me more the In System Programming ?

From: on behalf of Dave Hylands
Sent: Wed 3/1/2006 10:44 AM
Subject: Re: [Gumstix-users] roboAudio-th

Hi Joseph,

> Thanks, I find those 7 files but it didnt't solve my question because my
> background is too week.  I want to find out first is the pin lay out.
> has the top view of roboaudio.  And tell me the topleft is
> PWM but I don't know which one is power which one is ground which one is
> signal.

I'm at work and don't have my roboaudio in front of me, so I'll
possibly elaborate a bit more when I get home tonight.

On the regular robostix, there are some labels on the back side of the
board to help out. I don't recall with the roboaudio.

I'm guessing that the PWM block is the same as on the regular
robostix, and that ground is the outside row of pins, V_MOTOR is the
middle row of pins, and the inside row of pins are the signals.

> And the next is motor.  For what kind of motor?  What are those two
> pins?  Power and ground?

The MOTOR pins are actually V_MOTOR, for connecting up a separate
motor supply. Even servo motors draw more current than the robostix
power supply can source, and you often want to run the servos at a
different voltage than +5, so a separate power connector was provided.
On the regular robostix there's a jumper to the regular +5, I'll have
to check what's on the roboaudio.

As a general rule, you can't connect any type of motor directly to the
robostix, but you can connect a motor controller. Servos have built-in
motor controller, so they work out OK. Any other type of motor is
going to require an H-Bridge (or other motor controller).

> Then GPIO, which is signal which is ground?

I think that the little white square in each corner of the silkscreen
is pin 1. On the GPIO_5V_B block (see Sheet 2 of the schematic) there
is no ground.

> Next is ATMEGA?  What is it?  How to use it?

That's ADC_ATMEGA, which are 8 ADC's (analog to digital converters)
connected to the ATMega128. There's sample code posted (see links from
the Robostix-Programming page)

> Next is audio.  Why 6 pins? 5.1 Channel? which is which?

See Sheet 5 of the schematic. Looks like a ground (pin 4) Stero Line
in (pins 2 & 6), Stereo out (pins 1 & 5), and VREFDRV (not sure -
check the datasheet on the UCB1400).

> 16 pins in UARTS,  What are they?

Well there's a 4 pin TTL UART from the gumstix (STUART - ttyS2). There
are also 2 UARTs from the ATMega128 and an i2c (which connects to both
the gumstix and atmega)/

> What is ISP?

That's the In System Programming header for programming the atmega if
you're going to use the roboaudio by itself.

> What is the 4 pins GUMSTIX for?

Thats the console from the gumstix (als a UART - ttyS0)

This page describes many of the signals (but for the robostix)

I'll see about adding a section which formats it in the connector
order that they appear in for the roboaudio.

The PWM, UARTS, gumstix, and ISP connectors are identical for the
roboaudio and the robostix.

Dave Hylands
Vancouver, BC, Canada

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