SCANSTA111 National Semiconductor Corporation, SCANSTA111 Datasheet - Page 7

• Manufacturer Part Number: SCANSTA111
• Description: Enhanced Scan Bridge Multidrop Addressable Ieee 1149.1 Jtag Port
• Manufacturer: National Semiconductor Corporation

State Machines
The ’STA111 contains three distinct but coupled state-
machines (see Figure 2). The first of these is the TAP-control
state-machine, which is used to drive the ’STA111s scan
ports in conformance with the 1149.1 Standard. The second
is the ’STA111-selection state-machine (Figure 3). The third
state-machine actually consists of three identical but inde-
pendent state-machines (see Figure 4), one per ’STA111
The ’STA111’s scan port-configuration state-machine is used
to control the insertion of local scan ports into the overall
scan chain, or the isolation of local ports from the chain.
From the perspective of a system’s (single) scan controller,
each ’STA111 presents only one scan chain to the master.
The ’STA111 architecture allows one or more of the
’STA111’s local ports to be included in the active scan chain.
Each local port can be parked in one of four stable states
(Parked-TLR, Parked-RTI, Parked-Pause-DR or Parked-
Pause-IR), either individually or simultaneously with other
local ports. Parking a chain removes that local chain from the
(Continued)
FIGURE 4. Local SCANSTA111 Port Configuration State Machine
FIGURE 3. State Machine for SCANSTA111 Selection Controller
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local scan port. Each of these scan port selection state-
machines allows individual local ports to be inserted into and
removed from the ’STA111s overall scan chain.
The ’STA111 selection state-machine performs the address
matching which gives the ’STA111 its multi-drop capability.
That logic supports single-’STA111 access, multi-cast, and
broadcast. The ’STA111-selection state-machine imple-
ments the chip’s Level-1 protocol.
active scan chain. Conversely, a parked chain can be un-
parked, causing the corresponding local port to be inserted
into the active scan chain.
As shown in Figure 4, the ’STA111’s three scan port-
configuration state-machines allow each of the part’s local
ports to occupy a different state at any given time. For
example, some ports may be parked, perhaps in different
states, while other ports participate in scan operations. The
state-diagram shows that some state transitions depend on
the current state of the TAP-control state-machine. As an
example, a local port which is presently in the Parked-RTI
state does not become unparked (i.e., enter the Unparked
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