I'm measuring 70mv RMS noise at pin40 with respect to pin20, the fundamental is ~= 20mhz with a strong (i'd say -6db) 40mhz harmonic. If I measure across the decoupling cap for the MAX232 I'm reading 17mv rms. The harmonic is of a lower amplitude, but appears to be about 100mhz. I've reached the end of my 60mhz Tek 2213A's capabilities now. ;)
My Clock is 22.18mhz, so i suspect the real values are 22.118 & 44.236
I'm going to try an additional 470pf (COG) from pin20 to the power plane, and 470pf from Pin 40 to the GND plane, but not tonight. I'll update with the results tomorrow. If that fails mabey I'll wire in a 1488 & a 1489 (& a +/- 15V supply) and see if that helps.
Thanks a bunch.