參數(shù)資料
型號: CY7C1522JV18-250BZI
廠商: CYPRESS SEMICONDUCTOR CORP
元件分類: SRAM
英文描述: 8M X 8 DDR SRAM, 0.45 ns, PBGA165
封裝: 15 X 17 MM, 1.40 MM HEIGHT, MO-216, FBGA-165
文件頁數(shù): 5/27頁
文件大?。?/td> 658K
代理商: CY7C1522JV18-250BZI
CY7C1522JV18, CY7C1529JV18
CY7C1523JV18, CY7C1524JV18
Document #: 001-44700 Rev. *B
Page 13 of 27
IDCODE
The IDCODE instruction loads a vendor-specific, 32-bit code into
the instruction register. It also places the instruction register
between the TDI and TDO pins and shifts the IDCODE out of the
device when the TAP controller enters the Shift-DR state. The
IDCODE instruction is loaded into the instruction register at
power up or whenever the TAP controller is supplied a
Test-Logic-Reset state.
SAMPLE Z
The SAMPLE Z instruction connects the boundary scan register
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 supplied 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 input and output pins is captured
in the boundary scan register.
The TAP controller clock only operates 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 then tried 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, stabilize the SRAM long enough to meet
the TAP controller's capture setup plus hold times (tCS and tCH).
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.
After 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 places an initial data pattern at the latched parallel
outputs of the boundary scan register cells before the selection
of another boundary scan test operation.
The shifting of data for the SAMPLE and PRELOAD phases
occurs concurrently when required, that is, while the data
captured is shifted out, the preloaded data is 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 drives the preloaded data out through
the system output pins. This instruction also connects the
boundary scan register 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 108.
When this scan cell, called the ‘extest output bus tri-state’, is
latched into the preload register during the Update-DR state in
the TAP controller, it directly controls the state of the output
(Q-bus) pins, when the EXTEST is entered as the current
instruction. When HIGH, it enables the output buffers to drive the
output bus. When LOW, this bit places the output bus into a
High-Z condition.
This bit is set by entering the SAMPLE/PRELOAD or EXTEST
command, and then shifting the desired bit into that cell, during
the Shift-DR state. During Update-DR, the value loaded into that
shift-register cell latches into the preload register. When the
EXTEST instruction is entered, this bit directly controls the output
Q-bus pins. Note that this bit is pre-set LOW to enable the output
when the device is powered up, and also when the TAP controller
is in the Test-Logic-Reset state.
Reserved
These instructions are not implemented but are reserved for
future use. Do not use these instructions.
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