IS61NLF204836B Datasheet, PDF (26/38 Pages) Integrated Silicon Solution, Inc – 100 percent bus utilization

IS61NLF204836B/IS61NVF/NVVF204836B
IS61NLF409618B/IS61NVF/NVVF409618B 
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 buf-
fers. The SRAM does not implement the 1149.1 commands
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. Instruc-
tions 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 control-
ler 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 instruc-
tions, 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 implemented, so
the TAP controller is not fully 1149.1 compliant. When the
SAMPLE/PRELOAD instruction is loaded to the instruc-
tion 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 oper-
ates 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 instruc-
tion 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.
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Integrated Silicon Solution, Inc. — www.issi.com
Rev. 00C
02/20/2013