Altera Virtual JTAG IP Core - Manual (Page 9)

This state information, including a bank of enable signals, is forwarded to each of the SLD nodes. The SLD
nodes perform the updates to the VIR and VDR according to the control states provided by the
sld_hub
.
The SLD nodes are responsible for maintaining continuity between the
TDI
and
TDO
pins.
The figure below shows the SLD hub finite state machine. There is no direct state signal available to use for
application design.
Figure 6: sld_hub Finite State Machine
USR0 USR1
JTAG_Test_Logic_Reset
JTAG_Run_Test_Idle Virtual_Select_DR_Scan (1) Virtual_Select_IR_Scan (1)
Virtual_Capture_DR
Virtual_Shift_DR
Virtual_Exit1_DR
Virtual_Pause_DR
Virtual_Exit2_DR
Virtual_Update_DR
Virtual_Capture_IR
Virtual_Shift_IR (1)
Virtual_Exit1_IR (1)
Virtual_Pause_IR (1)
Virtual_Exit2_IR (1)
Virtual_Update_IR
Description of the Virtual JTAG Interface
The Virtual JTAG Interface implements an SLD node interface, which provides a communication interface
to the JTAG port. The megafunction exposes control signals that are part of the SLD hub; namely, JTAG
port signals, all finite state machine controller states of the TAP controller, and the SLD hub finite state
machine. Additionally, each instance of the Virtual JTAG megafunctions contain the virtual Instruction
Register for the SLD node. Instantiation of this megafunction automatically infers the SLD infrastructure,
and one SLD node is added for each instantiation.
The Virtual JTAG megafunction provides a port interface that mirrors the actual JTAG ports. The interface
contains the JTAG port pins, a one-hot decoded output of all JTAG states, and a one-hot decoded output
of all the virtual JTAG states. Virtual JTAG states are the states decoded from the SLD hub finite state
machine. The
ir_in
and
ir_out
ports are the parallel input and output to and from the VIR. The VIR ports
are used to select the active VDR datapath. The JTAG states and
TMS
output ports are provided for debugging
purposes only. Only the virtual JTAG, TDI , TDO , and the IR signals are functional elements of the
megafunction. When configuring this megafunction using the MegaWizard ™ Plug-In Manager, you can
hide TMS and the decoded JTAG states.
Altera Corporation Virtual JTAG Megafunction (sld_virtual_jtag)
Send Feedback
9 Description of the Virtual JTAG Interface
UG-SLDVRTL
2014.03.19