Altera Corporation
9–13
January 2008
Stratix II Device Handbook, Volume 2
IEEE 1149.1 (JTAG) Boundary-Scan Testing for Stratix II and Stratix II GX Devices
During the capture phase, multiplexers preceding the capture registers
select the active device data signals. This data is then clocked into the
capture registers. The multiplexers at the outputs of the update registers
also select active device data to prevent functional interruptions to the
device. During the shift phase, the boundary-scan shift register is formed
by clocking data through capture registers around the device periphery
and then out of the TDO pin. The device can simultaneously shift new test
data into TDI and replace the contents of the capture registers. During the
update phase, data in the capture registers is transferred to the update
registers. This data can then be used in the EXTEST instruction mode.
Figure 9–9 shows the SAMPLE/PRELOAD waveforms. The
SAMPLE/PRELOAD
instruction code is shifted in through the TDI pin. The
TAP controller advances to the CAPTURE_DR state and then to the
SHIFT_DR
state, where it remains if TMS is held low. The data that was
present in the capture registers after the capture phase is shifted out of the
TDO
pin. New test data shifted into the TDI pin appears at the TDO pin
after being clocked through the entire boundary-scan register.
Figure 9–9shows that the instruction code at TDI does not appear at the TDO pin
until after the capture register data is shifted out. If TMS is held high on
two consecutive TCK clock cycles, the TAP controller advances to the
UPDATE_DR
state for the update phase.
Figure 9–9. SAMPLE/PRELOAD Shift Data Register Waveforms
EXTEST Instruction Mode
The EXTEST instruction mode is used primarily to check external pin
connections between devices. Unlike the SAMPLE/PRELOAD mode,
EXTEST
allows test data to be forced onto the pin signals. By forcing
known logic high and low levels on output pins, opens and shorts can be
detected at pins of any device in the scan chain.
Data stored in
boundary-scan
register is shifted
out of TDO.
After boundary-scan
register data has been
shifted out, data
entered into TDI will
shift out of TDO.
UPDATE_IR
SHIFT_DR
EXIT1_DR
SELECT_DR
CAPTURE_DR
EXIT1_IR
UPDATE_DR
SHIFT_IR
Instruction Code
TCK
TMS
TDI
TDO
TAP_STATE