CY7C1386DV25, CY7C1386FV25
CY7C1387DV25, CY7C1387FV25
Document Number: 38-05548 Rev. *E
Page 13 of 30
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 balls. The
advantage of the BYPASS instruction is that it shortens the
boundary scan path when multiple devices are connected
together on a board.
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 #85
(for 119-BGA package) or bit #89 (for 165-fBGA package).
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 will directly control the state of the output
(Q-bus) pins, when the EXTEST is entered as the current
instruction. When HIGH, it will enable the output buffers to
drive the output bus. When LOW, this bit will place the output
bus into a High-Z condition.
This bit can be 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 will latch into the preload
register. When the EXTEST instruction is entered, this bit will
directly control the output Q-bus pins. Note that this bit is
preset HIGH 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.
TAP Timing
t
TL
Test Clock
(TCK)
1
2
3
4
5
6
Test Mode Select
(TMS)
tTH
Test Data-Out
(TDO)
tCYC
Test Data-In
(TDI)
tTMSH
tTMSS
tTDIH
tTDIS
tTDOX
tTDOV
DON’T CARE
UNDEFINED
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