CY7C1354DV25
CY7C1356DV25
Document #: 001-48974 Rev. *A
Page 11 of 29
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 Figure 1. TDI is internally
pulled up and can be unconnected if the TAP is unused in an
application. TDI is connected to the most significant bit (MSB) of
any register. (See Figure 2.)
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. The output changes on the falling edge
of TCK. TDO is connected to the least significant bit (LSB) of any
register. (See Figure 1.)
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.
During 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 TAP Controller Block Diagram.
During 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 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 (VSS)
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.
Figure 2. TAP Controller Block Diagram
Bypass Register
0
Instruction Register
0
1
2
Identification Register
0
1
2
29
30
31
.
.
.
Boundary Scan Register
0
1
2
.
.
x
.
.
.
Selection
Circuitry
Selection
Circuitry
TCK
TMS
TAP CONTROLLER
TDI
TD O
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