PRELIMINARY
CY7C1330AV25
CY7C1332AV25
Document No: 001-07844 Rev. *A
Page 7 of 19
EXTEST
EXTEST is a mandatory 1149.1 instruction which is to be
executed whenever the instruction register is loaded with all
0s. EXTEST is not implemented in this SRAM TAP controller,
and therefore this device is not compliant to 1149.1. The TAP
controller does recognize an all-0 instruction.
When an EXTEST instruction is loaded into the instruction
register, the SRAM responds as if a SAMPLE/PRELOAD
instruction has been loaded. There is one difference between
the two instructions. Unlike the SAMPLE/PRELOAD
instruction, EXTEST places the SRAM outputs in a High-Z
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 pins 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 transition (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.
Reserved
These instructions are not implemented but are reserved for
future use. Do not use these instructions.
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