SCANSTA111 datasheet(7/31 Pages) NSC

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State Machines (Continued)

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

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.

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

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

10124506

FIGURE 3. State Machine for SCANSTA111 Selection Controller

10124507

FIGURE 4. Local SCANSTA111 Port Configuration State Machine

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