ADVANCE
4 MEG x 8, 4 MEG x 9, 2 MEG x 18, 1 MEG x 36
1.8V VDD, HSTL, QDRIIb2 SRAM
ter, and through the TDI and TDO balls. To execute the
instruction once it is shifted in, the TAP controller
needs to be moved into the Update-IR state.
The user must be aware that the TAP controller
clock can only operate at a frequency up to 10 MHz,
while the SRAM clock operates more than an order of
magnitude faster. Because there is a large difference in
the clock frequencies, it is possible that during the
Capture-DR state, an input or output will undergo a
transition. The TAP may then try to capture a signal
while in transition (metastable state). This will not
harm the device, but there is no guarantee as to the
value that will be captured. Repeatable results may not
be possible.
EXTEST
The EXTEST instruction allows circuitry external to
the component package to be tested. Boundary scan
register cells at output balls are used to apply test vec-
tors, while those at input balls capture test results. Typ-
ically, the first test vector to be applied using the
EXTEST instruction will be shifted into the boundary
scan register using the PRELOAD instruction. Thus,
during the Update-IR state of EXTEST, the output drive
is turned on and the PRELOAD data is driven onto the
output pins.
To guarantee that the boundary scan register will
capture the correct value of a signal, the SRAM signal
must be stabilized long enough to meet the TAP con-
t
troller’s capture setup plus hold time (tCS plus CH).
The SRAM clock input might not be captured correctly
if there is no way in a design to stop (or slow) the clock
during a SAMPLE/PRELOAD instruction. If this is an
issue, it is still possible to capture all other signals and
simply ignore the value of the C and C#, and K and K#,
captured in the boundary scan register.
Once the data is captured, it is possible to shift out
the data by putting the TAP into the Shift-DR state.
This places the boundary scan register between the
TDI and TDO balls.
IDCODE
The IDCODE instruction causes a vendor-specific,
32-bit code to be loaded into the instruction register. It
also places the instruction register between the TDI
and TDO balls and allows the IDCODE to be shifted
out of the device when the TAP controller enters the
Shift-DR state. The IDCODE instruction is loaded into
the instruction register upon power-up or whenever
the TAP controller is given a test logic reset state.
BYPASS
SAMPLE Z
When the BYPASS instruction is loaded in the
instruction register and the TAP is placed in a Shift-DR
state, the bypass register is placed between the TDI
and TDO balls. The advantage of the BYPASS instruc-
tion is that it shortens the boundary scan path when
multiple devices are connected together on a board.
The SAMPLE Z instruction causes the boundary
scan register to be connected between the TDI and
TDO balls when the TAP controller is in a Shift-DR
state. It also places all SRAM outputs into a High-Z
state.
SAMPLE/PRELOAD
RESERVED
These instructions are not implemented but are
reserved for future use. Do not use these instructions.
When the SAMPLE/PRELOAD instruction is loaded
into the instruction register and the TAP controller is in
the Capture-DR state, a snapshot of data on the inputs
and bidirectional balls is captured in the boundary
scan register.
36Mb: 1.8V VDD, HSTL, QDRIIb2 SRAM
MT54W2MH18B_A.fm - Rev 9/02
Micron Technology, Inc., reserves the right to change products or specifications without notice.
©2002, Micron Technology Inc.
21
MICRON [ MICRON TECHNOLOGY ]
