COM20020D datasheet(70/72 Pages) SMSC

70 / 72 page

The EF bit also controls the resolution of the

following issues from the COM20020 Rev. B:

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

COM20020D 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 COM20020D detects a

write operation to Tentative-ID or Node-ID

the Tentative-ID or Duplicate-ID for generating

the network MAP without any issues. This

change is Enabled/Disabled by the EF bit.

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.

COM20020D Scheda tecnica(PDF) 70 Page - SMSC Corporation