CY7C1470V25_12 CYPRESS [Cypress Semiconductor], CY7C1470V25_12 Datasheet - Page 15

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

IEEE 1149.1 Serial Boundary Scan (JTAG)
The
boundary scan test access port (TAP). This port operates in
accordance with IEEE Standard 1149.1-1990 but does not have
the set of functions required for full 1149.1 compliance. These
functions from the IEEE specification are excluded because their
inclusion places an added delay in the critical speed path of the
SRAM. Note that the TAP controller functions in a manner that
does not conflict with the operation of other devices using 1149.1
fully compliant TAPs. The TAP operates using JEDEC-standard
2.5 V or 1.8 V I/O logic levels.
The CY7C1470V25/CY7C1474V25 contains a TAP controller,
instruction register, boundary scan register, bypass register, and
ID register.
Disabling the JTAG Feature
It is possible to operate the SRAM without using the JTAG
feature. To disable the TAP controller, TCK must be tied LOW
(V
internally pulled up and may be unconnected. They may
alternately be connected to V
should be left unconnected. Upon power-up, the device will
come up in a reset state which will not interfere with the operation
of the device.
Test Access Port (TAP)
Test Clock (TCK)
The test clock is used only with the TAP controller. All inputs are
captured on the rising edge of TCK. All outputs are driven from
the falling edge of TCK.
Test Mode Select (TMS)
The TMS input is used to give commands to the TAP controller
and is sampled on the rising edge of TCK. It is allowable to leave
this ball unconnected if the TAP is not used. The ball is pulled up
internally, resulting in a logic HIGH level.
Test Data-In (TDI)
The TDI ball is used to serially input information into the registers
and can be connected to the input of any of the registers. The
register between TDI and TDO is chosen by the instruction that
is loaded into the TAP instruction register. For information on
loading the instruction register, see
Diagram on page
unconnected if the TAP is unused in an application. TDI is
connected to the most significant bit (MSB) of any register.
Test Data-Out (TDO)
The TDO output ball is used to serially clock data-out from the
registers. The output is active depending upon the current state
of the TAP state machine (see
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 (V
edges of TCK. This RESET does not affect the operation of the
SRAM and may be performed while the SRAM is operating.
Document Number: 38-05290 Rev. *O
SS
) to prevent clocking of the device. TDI and TMS are
CY7C1470V25/CY7C1474V25
17. TDI is internally pulled up and can be
DD
Instruction Codes on page
through a pull-up resistor. TDO
incorporates
TAP Controller State
DD
) for five rising
a
serial
21).
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 balls 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 register. Data is serially loaded into the TDI ball on the
rising edge of TCK. Data is output on the TDO ball 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 balls as shown in the
page
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 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
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
page
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
18. Upon power-up, the instruction register is loaded with
21.
Identification Register Definitions on
TAP Controller Block Diagram on
CY7C1470V25
CY7C1472V25
CY7C1474V25
Page 15 of 38
SS
)