COM20019I_06 Datasheet, PDF (64/65 Pages) SMSC Corporation – Low Cost ARCNET (ANSI 878.1) Controller with 2K x 8 On-Board RAM

Low Cost ARCNET (ANSI 878.1) 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 COM20019I 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 COM20019I 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.
Rev. 03-07-06
Page 64
DATASHEET
SMSC COM20019I