IS61NLF25636A Datasheet, PDF (25/37 Pages) Integrated Silicon Solution, Inc – 256K x 36 and 512K x 18 9Mb, FLOW THROUGH (NO WAIT) STATE BUS SRAM

IS61NLF25636A/IS61NVF25636A
IS61NLF51218A/IS61NVF51218A
ISSI ^®
TAP INSTRUCTION SET
Eight instructions are possible with the three-bit instruction
register and all combinations are listed in the Instruction
Code table. Three instructions are listed as RESERVED
and should not be used and the other five instructions are
described below. The TAP controller used in this SRAM is
not fully compliant with the 1149.1 convention because
some mandatory instructions are not fully implemented.
The TAP controller cannot be used to load address, data or
control signals and cannot preload the Input or Output
buffers. The SRAM does not implement the 1149.1 com-
mands EXTEST or INTEST or the PRELOAD portion of
SAMPLE/PRELOAD; instead it performs a capture of the
Inputs and Output ring when these instructions are executed.
Instructions are loaded into the TAP controller during the
Shift-IR state when the instruction register is placed
between TDI and TDO. During this state, instructions are
shifted from the instruction register through the TDI and
TDO pins. To execute an instruction once it is shifted in,
the TAP controller must be moved into the Update-IR
state.
EXTEST
EXTEST is a mandatory 1149.1 instruction which is to be
executed whenever the instruction register is loaded with
all 0s. Because EXTEST is not implemented in the TAP
controller, this device is not 1149.1 standard compliant.
The TAP controller recognizes an all-0 instruction. When
an EXTEST instruction is loaded into the instruction
register, the SRAM responds as if a SAMPLE/PRELOAD
instruction has been loaded. There is a difference between
the instructions, unlike the SAMPLE/PRELOAD instruction,
EXTEST places the SRAM outputs in a High-Z state.
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
pins 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.
SAMPLE-Z
The SAMPLE-Z instruction causes the boundary scan
register to be connected between the TDI and TDO pins
when the TAP controller is in a Shift-DR state. It also
places all SRAM outputs into a High-Z state.
SAMPLE/PRELOAD
SAMPLE/PRELOAD is a 1149.1 mandatory instruction.
The PRELOAD portion of this instruction is not imple-
mented, so the TAP controller is not fully 1149.1 compli-
ant. When the SAMPLE/PRELOAD instruction is loaded
to the instruction register and the TAP controller is in the
Capture-DR state, a snapshot of data on the inputs and
output pins is captured in the boundary scan register.
It is important to realize that the TAP controller clock
operates at a frequency up to 10 MHz, while the SRAM
clock runs more than an order of magnitude faster.
Because of the clock frequency differences, it is possible
that during the Capture-DR state, an input or output will
under-go a transition. The TAP may attempt a signal
capture while in transition (metastable state). The device
will not be harmed, but there is no guarantee of the value
that will be captured or repeatable results.
To guarantee that the boundary scan register will capture
the correct signal value, the SRAM signal must be
stabilized long enough to meet the TAP controller’s
capture set-up plus hold times (tCS and tCH). To insure that
the SRAM clock input is captured correctly, designs need
a way to stop (or slow) the clock during a SAMPLE/
PRELOAD instruction. If this is not an issue, it is possible
to capture all other signals and simply ignore the value of
the CLK 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 pins.
Note that since the PRELOAD part of the command is not
implemented, putting the TAP into the Update to the Update-DR
state while performing a SAMPLE/PRELOAD instruction
will have the same effect as the Pause-DR command.
BYPASS
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 pins.
The advantage of the BYPASS instruction is that it
shortens the boundary scan path when multiple devices
are connected together on a board.
RESERVED
These instructions are not implemented but are reserved
for future use. Do not use these instructions.
Integrated Silicon Solution, Inc. — www.issi.com — 1-800-379-4774
25
Rev. B
08/26/05