PCI7421 datasheet(89/298 Pages) TI

89 / 298 page

3−33

Therefore, in order to maintain consistent gap-counts throughout the bus, the following rules apply to the use of the

IBR bit, RHB, and Gap_Count in PHY register 1:

•

Following the transmission of a PHY-config packet, a bus reset must be initiated in order to verify that all

nodes have correctly updated their RHBs and Gap_Count values and to ensure that a subsequent new

connection to the bus causes the Gap_Count to be set to 63 on all nodes in the bus. If this bus reset is

initiated by setting the IBR bit to 1, then the RHB and Gap_Count field must also be loaded with the correct

values consistent with the just transmitted PHY-config packet. In the PCI7x21/PCI7x11 controller, the RHB

and Gap_Count are updated to their correct values upon the transmission of the PHY-config packet, so

these values may first be read from register 1 and then rewritten.

•

Other than to initiate the bus reset, which must follow the transmission of a PHY-config packet, whenever

the IBR bit is set to 1 in order to initiate a bus reset, the Gap_Count value must also be set to 63 so as to

be consistent with other nodes on the bus, and the RHB must be maintained with its current value.

•

The PHY register 1 must not be written to except to set the IBR bit. The RHB and Gap_Count must not be

written without also setting the IBR bit to 1.

PCI7421 데이터시트(PDF) 89 Page - Texas Instruments