Cypress Semiconductor CY7C1330AV25 Fiche technique - Page 7

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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

instruction has been loaded. There is one difference between

the

two

instructions.

Unlike

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

Document No: 001-07844 Rev. *A

PRELIMINARY

the

SAMPLE/PRELOAD

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

and t

). 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

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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