Franc Zabkar wrote in message
...
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
--
Please remove one 'i' from my address when replying by email.

I got back to this today. Saved to disc the existing (corrupted ?) data in
the serial EEPROM and cut the SDA line to the Ez-usb chip.
The EZbus mixer is no longer "Becoming Ezbus" and a blank screen.
But windows recognises a USB device connected and by UVCView/USB view the
USB is working up to the USB chip , reading

---===Device Information===---

ConnectionStatus:
Current Config Value: 0x00 - Device Bus Speed: Full
Device Address: 0x00
Open Pipes: 0
*!*ERROR: No open pipes!

===Device Descriptor===
bLength: 0x12
bDescriptorType: 0x01
bcdUSB: 0x0100
bDeviceClass: 0xFF - This is a Vendor Specific Device
bDeviceSubClass: 0xFF
bDeviceProtocol: 0xFF
bMaxPacketSize0: 0x40 = (64) Bytes
idVendor: 0x0547idProduct:
0x2131
bcdDevice: 0x0004
iManufacturer: 0x00
iProduct: 0x00
iSerialNumber: 0x00
bNumConfigurations: 0x01

ie Cypress VID/PID

Where to now? presumably forcing a pipe somehow