CY7C1354B
CY7C1356B
Document #: 38-05114 Rev. *C
Page 11 of 29
Diagram). The output changes on the falling edge of TCK.
TDO is connected to the Least Significant Bit (LSB) of any
register.
Performing a TAP Reset
A Reset is performed by forcing TMS HIGH (VDD) for five rising
edges of TCK. This RESET does not affect the operation of
the SRAM and may be performed while the SRAM is
operating. At power-up, the TAP is reset internally to ensure
that TDO comes up in a High-Z state.
TAP Registers
Registers are connected between the TDI and TDO pins and
allow data to be scanned into and out of the SRAM test
circuitry. Only one register can be selected at a time through
the instruction registers. Data is serially loaded into the TDI pin
on the rising edge of TCK. Data is output on the TDO pin on
the falling edge of TCK.
Instruction Register
Three-bit instructions can be serially loaded into the instruction
register. This register is loaded when it is placed between the
TDI and TDO pins as shown in the TAP Controller Block
Diagram. Upon power-up, the instruction register is loaded
with the IDCODE instruction. It is also loaded with the IDCODE
instruction if the controller is placed in a reset state as
described in the previous section.
When the TAP controller is in the Capture-IR state, the two
least significant bits are loaded with a binary “01” pattern to
allow for fault isolation of the board level serial test path.
Bypass Register
To save time when serially shifting data through registers, it is
sometimes advantageous to skip certain states. The bypass
register is a single-bit register that can be placed between TDI
and TDO pins. This allows data to be shifted through the
SRAM with minimal delay. The bypass register is set LOW
(VSS) when the BYPASS instruction is executed.
Boundary Scan Register
The boundary scan register is connected to all the input and
output pins on the SRAM. Several no connect (NC) pins are
also included in the scan register to reserve pins for higher
density devices. The ×36 configuration has a 69-bit-long
register, and the ×18 configuration has a 69-bit-long register.
The boundary scan register is loaded with the contents of the
RAM Input and Output ring when the TAP controller is in the
Capture-DR state and is then placed between the TDI and
TDO pins when the controller is moved to the Shift-DR state.
The EXTEST, SAMPLE/PRELOAD and SAMPLE Z instruc-
tions can be used to capture the contents of the Input and
Output ring.
The Boundary Scan Order tables show the order in which the
bits are connected. Each bit corresponds to one of the bumps
on the SRAM package. The MSB of the register is connected
to TDI, and the LSB is connected to TDO.
Identification (ID) Register
The ID register is loaded with a vendor-specific, 32-bit code
during the Capture-DR state when the IDCODE command is
loaded in the instruction register. The IDCODE is hardwired
into the SRAM and can be shifted out when the TAP controller
is in the Shift-DR state. The ID register has a vendor code and
other information described in the Identification Register
Definitions table.
TAP Instruction Set
Eight different instructions are possible with the three-bit
instruction register. All combinations are listed in the
Instruction Code table. Three of these instructions are listed
as RESERVED and should not be used. The other five instruc-
tions 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 Input or Output 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 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
through the instruction register through the TDI and TDO pins.
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 the TAP controller, and
therefore this device is not compliant to the 1149.1 standard.
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 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 instructions are loaded into 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.
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