10 Mbps ARCNET (ANSI 878.1) Controller with 2Kx8 On-Chip RAM
Datasheet
EF=0
Tx/Rx completed
TA/RI bit
Internal Setting Pulse
nINTR pin
prohibition period
Tx/Rx completed
EF=1
TA/RI bit
Internal Setting Pulse
nINTR pin
Figure 10.1 - Effect of the EF Bit on the TA/RI Bit
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 COM20022I 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 COM20022I 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.
SMSC COM20022I
Page 81
Revision 09-27-07
DATASHEET
SMSC [ SMSC CORPORATION ]
