Posted on May 17, 2011 at 12:07Hello,
we have a design successfully running that uses the DDC hardware of the uPSD3233A. We emulate a DVI compliant monitor with variable DDC information and this wirked fine, until now.
A customer of us has bought a new ATI Radeon 750 PCI express card. This card refuses to accept our DDC data.
When we anaylze the data stream with an oscilloscope we see the following:
1) Working case: PC send I2C command 0xA0, this is acknowledged by the DDC hardware of the uPSD.
2) Error case: PC (with PCI-Express card) send I2C command 0xA0,
no acknowledge is send by the DDC hardware. So the identification fails and the DVI output is switched off.
We see only one timing difference between the two cases: In the working case the I2C-clock is constand frequence (40 KHz) during the data and ACK phase. In the non working case, the I2C clock is 40 kHz for the 8 data bits and as fast as possible (short delay) for the ACk phase.
Has anybody else made some experiances with DDC on PCI express cards? As far as I can see there is not much software can help in this case. It seems to be a hardware problem of the DDC hardware of the uPSD. Or are we completely wrong?
Any kindof help is greatly appreciated (as is always is ;) ).
regards
Thomas
