CY7C1444AV33_10 Datasheet, PDF (12/28 Pages) Cypress Semiconductor – 36-Mbit (1 M × 36/2 M × 18) Pipelined DCD Sync SRAM 3.3 V core power supply

CY7C1444AV33
CY7C1445AV33
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 data path.
Bypass Register
To save time when serially shifting data through registers, it is
sometimes advantageous to skip certain chips. The bypass
register is a single-bit register that can be placed between the
TDI and TDO balls. This allows data to be shifted through the
SRAM with minimal delay. The bypass register is set LOW (V_SS)
when the BYPASS instruction is executed.
Boundary Scan Register
The boundary scan register is connected to all the input and
bidirectional balls on the SRAM.
The boundary scan register is loaded with the contents of the
RAM I/O ring when the TAP controller is in the Capture-DR state
and is then placed between the TDI and TDO balls when the
controller is moved to the Shift-DR state. The EXTEST,
SAMPLE/PRELOAD and SAMPLE Z instructions can be used to
capture the contents of the I/O 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
Overview
Eight different instructions are possible with the three bit
instruction register. All combinations are listed in the Instruction
Codes table. Three of these instructions are listed as
RESERVED and should not be used. The other five instructions
are described in detail below.
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.
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 pins when the TAP
controller is in a Shift-DR state. The SAMPLE Z command puts
the output bus into a high Z state until the next command is given
during the “Update IR” state.
SAMPLE/PRELOAD
SAMPLE/PRELOAD is a 1149.1 mandatory instruction. 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.
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 tran-
sition (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 times (t_CS and t_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 CK and CK 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.
PRELOAD allows an initial data pattern to be placed at the
latched parallel outputs of the boundary scan register cells prior
to the selection of another boundary scan test operation.
The shifting of data for the SAMPLE and PRELOAD phases can
occur concurrently when required—that is, while data captured
is shifted out, the preloaded data can be shifted in.
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.
EXTEST
The EXTEST instruction enables the preloaded data to be driven
out through the system output pins. This instruction also selects
the boundary scan register to be connected for serial access
between the TDI and TDO in the shift-DR controller state.
EXTEST OUTPUT BUS TRI-STATE
IEEE Standard 1149.1 mandates that the TAP controller be able
to put the output bus into a tri-state mode.
The boundary scan register has a special bit located at bit# 89
(for 165-ball FBGA packages).When this scan cell, called the
Document Number: 38-05352 Rev. *G
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