[DSP-10] Problems with Serial Shift Registers.

[Bob Larkin]

Hi Chuck,

Mike and I conversed a bit about your problem this AM. We decided that we 
could not think of a single problem that would create the situation that we 
believe exists.  That is:
*  Everything worked fine for 3 years, then
*  Incorrect outputs from U107 using UDIAG2 (Apparently shifted by one 
position)
*  Correct programming of the U104 126 MHz synthesizer
*  Incorrect programming of the 19.68 Synthesizer

Possibly the issue is related to the rise time of the data and clock from 
the KDSP10. The level shifter on that board does not provide fast rise time 
above 3 volts. This was not an issue for my DSPx DSP-10, but was for 
others. Have you done any of the fixes for this?  I just noticed that I 
cannot find this on the DSP-10 web pages and i will take steps to get it 
there.

The issue of the rise time shows up when the SPI data is being shifted out 
of U108 into U107. A simple help is to slow down the data to give extra 
time for the clock, done by adding a 0.002 uF cap from pin 8 to pin 14 of 
U107. There are vias connected to each of these pins to make top 
installation straightforward.

A more elegant, alternate solution came from Steve Bible, N7HPR, and I will 
repeat his whole discussion:
------------------------------------------------
The problem comes from the level shifters on the KDSP10 board (the
PI5C3245S).  Level shifting takes time, and you see this in your o'scope
traces as sloping traces on the Serial Clock (FL2) and Serial Data (FL0).

My solution was to use an additional 74HC14 DIP and piggy back it on top of
U3 on the KDSP10 board.  Bend pins 1 through 6 and 8 through 13 pins
straight out from the package.  Be careful not to stress the pin too much as
you bend it, they may break.  Clip off the narrow part of the pin and leave
the thick part of the pin.  Allow the power (pin 14) and ground (pin 7) pins
to stay the same, hanging down.  Piggy back the 74HC14 to the top of U3 by
soldering the power (pin 14) and ground (pin 7) pins to the same on U3.
This provides power and ground to the top 74HC14.

Connect a wire from P2-4 (FL2) on the KDSP10 to pin 13 of the piggy back
74HC14.  Connect a wire from pin 12 to 11.  Connect a wire from pin 10 to
the through hole capacitor for FL2.

Connect a wire from P2-3 (FL0) on the KDSP10 to pin 1 of the piggy back
74HC14.  Connect a wire from pin 2 to 3.  Connect a wire from pin 4 to the
through hole capacitor for FL0.
  ------------------------------------------------

The above, of course, does not relate to the 19.68 synthesizer. Also, I 
suspect this is old news, but all I have for now!

73,
Bob  W7PUA