"Why you want tristate? It is an undefined logic level. The receiver may see HIGH or LOW, or oscillation..."
--> when it is tri-stated other output will be connected to receiver.
Actual case is,
I have a JTAG chain, with 2 devices connected to a connector (where an ICE or equalent will access the chain to program each device one by one).
Device 1 - 3.3V device
Device 2 - 1.8V device(last in chain)
I need to have option to bypass device2 when required.
TCK,TMS,TST & TDO going to Device2 are going to voltage translating switch(SN74AVC4T245 - name U1) - this translates 3.3V logic to 1.8V logic.
which can disabled by driving OE#
Device1 TDO - can go to Device 2 TDI(in image above it is OUT2) through voltage translating buffer (Device1,Device2 both are in chain) or directly to Connector TDI(when Device2 bypassed- in image it is OUT1)
to implement this,i need a demux(U2)
Case1 : Device2 is bypassed in chain - demux will send IN to Out1
Out2 will be tri-stated,and U1 also disabled by driving OE# of U1
Case2: Device1,Device2 are in chain
demux will select Out2 (from IN),
Out1 will be tristate and U1 will be enabled(OE# LOW), because U1 is enabled TDO from device2 will go to TDO of the connector.