Debug and Test Interface
14-10
GMS30C7201 Data Sheet
There is no parallel output from the bypass register.
A logic 0 is loaded from the parallel input of the bypass register in the CAPTURE-DR
state.
Boundary Scan (BS) Register
Purpose: The BS register consists of a serially connected set of cells around the
periphery of the device, at the interface between the core logic and the system input/
output pads. This register can be used to isolate the core logic from the pins and then
apply tests to the core logic, or conversely to isolate the pins from the core logic and
then drive or monitor the system pins. Operating modes: The BS register is selected as
the register to be connected between
TDI
and
TDO
only during the SAMPLE/
PRELOAD, EXTEST and INTEST instructions. Values in the BS register are used, but
are not changed, during the CLAMP and CLAMPZ instructions. In the normal (system)
mode of operation, straight-through connections between the core logic and pins are
maintained and normal system operation is unaffected. In TEST mode (i.e. when either
EXTEST or INTEST is the currently selected instruction), values can be applied to the
core logic or output pins independently of the actual values on the input pins and core
logic outputs respectively. On the GMS30C7201 all of the boundary scan cells include
an update register and thus all of the pins can be controlled in the above manner.
Additional boundary-scan cells are interposed in the scan chain in order to control the
enabling of tristateable buses. The values stored in the BS register after power-up are
not defined. Similarly, the values previously clocked into the BS register are not
guaranteed to be maintained across a Boundary Scan reset (from forcing
nTRST
LOW
or entering the Test Logic Reset state).
Single-step Operation
GMS30C7201 is a static design and there is no minimum clock speed. It can therefore
be single-stepped while the INTEST instruction is selected and the PLLs are bypassed.
This can be achieved by serializing a parallel stimulus and clocking the resulting serial
vectors into the boundary-scan register. When the boundary-scan register is updated,
new test stimuli are applied to the core logic inputs; the effect of these stimuli can then
be observed on the core logic outputs by capturing them in the boundary-scan register.