Cypress CY7C1473V25, CY7C1475V25, CY7C1471V25 manual TAP Timing, Bypass

CY7C1471V25

CY7C1473V25

CY7C1475V25

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 time (tCS plus 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 CLK 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 balls.

Note that since the PRELOAD part of the command is not implemented, putting the TAP to the Update-DR state while performing a SAMPLE/PRELOAD instruction has the same effect as the Pause-DR command.

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 balls. 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.

TAP Timing

1	2		3
Test Clock
(TCK )	tTH	tTL	tCY C
tTM SS	tTM SH

Test M ode Select (TM S)

tTDIS tTDIH

Test Data-In (TDI)

Test Data-Out (TDO)

DON’T CA RE

4 5 6

tTDO V

tTDOX

UNDEFINED

Document #: 38-05287 Rev. *I Page 15 of 32

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