Hello,
Electronics newbie with a question. I have a DAQ card which is communicating with 8 perif boards over a SCSI bus. The communication is controlled by a 20Mhz TTL clock over one of the bus lines. The DAQ card has the option to have this clock internally generated by the DAQ card or by feeding it an external clock. For my application it will be necessary to feed the DAQ an external clock. I have noted the following:
1) When looking at the internally generated clock over the bus on a scope it looks perfect, 0-5V TTL.2) When looking at my externally generated clock over the bus on the scope (the exteral clock also supplies a TTL 20Mhz signal with the same available power as the DAQ clock) the clock signal no longer looks squarish but rather deformed looking with a sort of ringing/extra occilating like behavior. As a note, the external clock looks fine on the scope when not fed onto the bus.
Does anyone have any ideas as to why the external would look strange like this on the bus while the DAQ supplied clock looks fine on the bus even though they can supply the same amount of power? As a last note the SCSI bus consists of 9 cables:
1 cable that has 9 connector taps ~1 inch spacing, 1 tap for the daq and 8 taps for the additional 8 cables which are each 6 inches long and feed the individual perif boards.Thanks for any suggestions on this,
Kev