AR# 175


XC4000H: Why are there two tristate pins (TP and TS ) on the 4000H IOBs?


The 4000H IOBs were created by basically splitting each existing
4000 IOB in two.


Because of this, a need arose to create a new tristate pin,
as only one existed in the original IOB, and one was needed for each of the
newly created IOBs. Since the flip flops are taken out of the 4000H IOBs,
the clock line became the second tristate pin. Thus, the two tristate pins
had access to different routing resources, as shown below:

- TP used to be the T pin in the 4k IOB, it has better access to global

- TS used to be the clock pin of the 4k IOB, it has better "parallel connection"
(i.e. if many IOBs need be tristated, this is the pin to use)

- There is no hidden tristate control as in the 4k IOB. I.e. There is no
OBUF, there is only an OBUFT. PPR needs to route to the TS pin in order to
disable the tristate to create an obuf.

- There shouldn't be a case where an IOB gets both signals routed to it.

AR# 175
Date 10/01/2008
Status Archive
Type General Article
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