COM20022ITQFP datasheet(82/83 Pages) SMSC

82 / 83 page

10 Mbps ARCNET (ANSI 878.1) Controller with 2Kx8 On-Board RAM

Datasheet

Rev. 08-18-03

Page 82

SMSC COM20022I

DATASHEET

Tx/Rx completed

TA/RI bit

Internal Setting Pulse

nINTR pin

prohibition period

EF=1

Tx/Rx completed

TA/RI bit

Internal Setting Pulse

nINTR pin

EF=0

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

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.

COM20022ITQFP Datasheet(PDF) 82 Page - SMSC Corporation