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SCANPSC110FSC

SCAN Bridge Hierarchical and Multidrop Addressable JTAG Port (IEEE1149.1 System Test Support)

Fairchild Semiconductor 

Overview of SCANPSC110F Bridge Functions (Continued)

FIGURE 4. Local SCANPSC110F Bridge Port Configuration State Machine

The SCANPSC110F’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 SCANPSC110F presents only one

scan chain to the master. The SCANPSC110F architecture

allows one or more of the SCANPSC110F’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

“unparked”, causing the corresponding local port to be

inserted into the active scan chain.

As shown in Figure 4, the SCANPSC110F'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

state) until the SCANPSC110F receives an UNPARK

instruction and the SCANPSC110F's TAP state-machine

enters the Run-Test/Idle state.

Similarly, certain transitions of the scan port-configuration

state-machine can force the SCANPSC110F's TAP-control

state-machine into specific states. For example, when a

local port is in the Unparked state and the SCANPSC110F

receives a PARKRTI instruction, the Local Port controller

enters the Parked-RTI state in which TMSLn will be held

LOW until the port is later unparked. While TMSLn is held

LOW, all devices on that local scan chain remain in their

current TAP State (the RTI TAP controller state in this

example).

The SCANPSC110F's scan port-configuration state-

machine implements part of the SCANPSC110F's Level-2

protocol. In addition, the SCANPSC110F provides a num-

ber of Level-2 instructions for functions other than local

scan port configuration. These instructions provide access

to and control of various registers within the

SCANPSC110F. This set instructions includes:

BYPASS

CNTRSEL

EXTEST

LFSRON

SAMPLE/PRELOAD

LFSROFF

IDCODE

CNTRON

MODESEL

CNTROFF

MCGRSEL

GOTOWAIT

LFSRSEL

Figure 5 illustrates how the SCANPSC110F's state-

machines interact. The SCANPSC110F-selection state-

machine enables or disables operation of the chip's three

port-selection state-machines. In SCANPSC110Fs which

are selected via Level-1 protocol (either as individual

SCANPSC110Fs or as members of broadcast or multi-cast

groups), Level-2 protocol commands can be used to park

or unpark local scan ports. Note that most transitions of the

port-configuration state-machines are gated by particular

states of the SCANPSC110F's TAP-control state-machine,

as shown in Figures 4, 5.

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