On Wed, 5 May 2010 08:56:58 +0100, "N_Cook" put
finger to keyboard and composed:

that 1K5 will have to go back in , It is the first point of recognition for
USB linking. Next to find why DISCON is permanently H.

My understanding is that the pullup resistor on D+ signals to the host
(your PC) that a USB device has been plugged in. The host then
attempts to enumerate (ie identify) the device.

If the device takes too long to go through its POST and initialisation
routines, then the host may time out. In such cases the device may
implement an active pullup which is disabled during its POST. When the
device is ready, the pullup resistor is enabled, allowing enumeration
to begin.

AIUI, the normal state of DISCON# is high.

See this EZ-USB Development Board (circuit on pages 5 & 6):
http://www.minford.ca/MF3001EZUSBManual.pdf

I found this detailed document:

The EZ-USB USB Integrated Circuit Technical Reference:
http://www.digchip.com/data/115/115-00027-0-AN2121S.pdf

It states that EZ-USB devices can power up in RAM-only mode, in which
case the host downloads runtime code into the 8051 CPU's internal 8K
RAM. During this time the device identifies itself as a "Default USB
Device". After the code has been downloaded, the device disconnects
and then reconnects, this time renumerating as the device defined
within the downloaded code.

Page 41 describes the EA (external access) pin. I think this may be
the key to how the device behaves. The tech ref also talks about mask
ROMed versions. Perhaps there is a way to force the EZ-USB chip into
RAM-only mode??? If so, then this will remove any corrupt firmware
from the equation. You could then use UVCView to see how the device
enumerates under these circumstances.

You could also disconnect the serial EEPROM, if any. The EEPROM would
contain Product and Vendor IDs for the manufacturer of the mixer. If
the EEPROM is absent, then the EZ-USB chip will ID with the PID and
VID of 0x0547 (Cypress Semiconductor) and 0x2131 (EZ-USB),
respectively.

- Franc Zabkar
--
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