--------------------------------------------------------------------------------

This modification enables the 3 pins next to the power connector for
the connection of an oscilliscope to view an eye pattern for line diagnostics.

Lars J Poulsen (lars@login.dkuug.dk) wrote:
"The eye pattern is a graphical tool for displaying certain internal
parameters from the digital signal recovery in a V.32(bis) modem.
A table of intermediate results is fed into a pair of digital-to-analog 
converter channels, which can be connected to the X Y Z inputs of an
oscilloscope in X/Y mode.  This displays a characteristic pattern of dots
when the modem is trained."

Note: these 2 chips are CMOS devices and are static sensitive.  Use
suitable caution.

chip Number     Part Number     Manufacturer            Description
--------------------------------------------------------------------------
U11             AD7528JN        (Analog Devices)        8-bit buffered DAC
U12             TL072CP         Texas Instruments       2 x FET op-amp

Paul Cantrell (paul@bosserv.bos.locus.com) called ZyXEL USA to modify his 
S/S+ modem to display the eye pattern.  Apparently ZyXEL USA no longer does 
the modifications any more.  The demand for this service was requested so 
infrequently that they don't have the traces on the new boards.

================================================================================
--
Robert Wong Jr.
1921 East 61st Avenue, Vancouver, B.C., Canada, V5P 2K2, (604) 322-6918
rwong@direct.ca or wrob@unixg.ubc.ca
Keeper of the ZyXEL FAQ and Head of the UBC-NeXT Users Group
Standard disclaimers apply.