CY7C1470V25_12 CYPRESS [Cypress Semiconductor], CY7C1470V25_12 Datasheet - Page 16

• Manufacturer Part Number: CY7C1470V25_12
• Manufacturer: CYPRESS [Cypress Semiconductor]

RESERVED and should not be used. The other five instructions
are described in detail below.
The TAP controller used in this SRAM is not fully compliant to the
1149.1 convention because some of the mandatory 1149.1
instructions are not fully implemented.
The TAP controller cannot be used to load address data or
control signals into the SRAM and cannot preload the I/O buffers.
The SRAM does not implement the 1149.1 commands EXTEST
or INTEST or the PRELOAD portion of SAMPLE/PRELOAD;
rather, it performs a capture of the I/O 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 through the
instruction register 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.
EXTEST
EXTEST is a mandatory 1149.1 instruction which is to be
executed whenever the instruction register is loaded with all 0s.
EXTEST is not implemented in this SRAM TAP controller, and
therefore this device is not compliant to 1149.1. The TAP
controller does recognize 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 one difference between the
two 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 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.
SAMPLE Z
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.
Document Number: 38-05290 Rev. *O
SAMPLE/PRELOAD
SAMPLE/PRELOAD is a 1149.1 mandatory instruction. The
PRELOAD portion of this instruction is not implemented, so the
device TAP controller is not fully 1149.1 compliant.
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.
The user must be aware that the TAP controller clock can only
operate at a frequency up to 20 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.
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 controller’s capture set-up plus
hold time (t
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 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 balls.
Note that since the PRELOAD part of the command is not
implemented, putting the TAP 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 balls. 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.
CS
plus t
CH
).
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