CY7C1354DV25 Datasheet, PDF (12/29 Pages) Cypress Semiconductor – 9-Mbit (256K x 36/512K x 18) Pipelined SRAM with NoBL Architecture

CY7C1354DV25
CY7C1356DV25
TAP Instruction Set
Overview
Eight different instructions are possible with the three bit
instruction register. All combinations are listed in the Identifi-
cation 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 after it is shifted in, the TAP controller must 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
during 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 undergoes a
transition. The TAP may then try to capture a signal while in
transition (metastable state). This does not harm the device, but
there is no guarantee as to the value that is captured.
Repeatable results may not be possible.
To guarantee that the boundary scan register captures the
correct value of a signal, the SRAM signal must be stabilized
long enough to meet the TAP controller's capture setup 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.
When 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.
Reserved
These instructions are not implemented but are reserved for
future use. Do not use these instructions.
Document #: 001-48974 Rev. *A
Page 12 of 29
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