COM20020_00 Datasheet, PDF (80/82 Pages) SMSC Corporation – Universal Local Area Network Controller with 2K x 8 On-Board RAM

The EF bit also controls the resolution of the
following issues from the COM20020 Rev. B:
A) Network MAP Generation
Tentative ID is used for generating the Network
MAP, but it sometimes detects a non-existent
node. Every time the Tentative-ID register is
written, the effect of the old Tentative-ID remains
active for a while, which results in an incorrect
network map. It can be avoided by a carefully
coded software routine, but this requires the
programmer to have deep knowledge of how the
COM20020 works. Duplicate-ID is mainly used
for generating the Network MAP. This has the
same issue as Tentative-ID.
A minor logic change clears all the remaining
effects of the old Tentative-ID and the old
Duplicate-ID, when the COM20020 detects a
write operation to Tentative-ID or Node-ID
register. With this change, programmers can use
the Tentative-ID or Duplicate-ID for generating
the network MAP without any issues. This
change is Enabled/Disabled by the EF bit.
B) Mask Register Reset
The Mask register is reset by a soft reset in the
COM20020 Rev. A, but is not reset in Rev. B.
The Mask register is related to the Status and
Diagnostic register, so it should be reset by a
soft reset. Otherwise, every time the soft reset
happens, the COM20020 Rev. B generates an
unnecessary interrupt since the status bits RI
and TA are back to one by the soft reset.
This is resolved by changing the logic to reset
the Mask register both by the hard reset and by
the soft reset. The soft reset is activated by the
Node-ID register going to 00h or by the RESET
bit going to High in the Configuration register.
This solution is Enabled/Disabled by the EF bit.
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