IEEE 1149.1 (JTAG) Boundary-Scan Testing for Cyclone II Devices
EXTESTselects data differently than SAMPLE/PRELOAD. EXTESTchooses
data from the update registers as the source of the output and output
enable signals. Once the EXTESTinstruction code is entered, the
multiplexers select the update register data. Thus, data stored in these
registers from a previous EXTESTor SAMPLE/PRELOADtest cycle can be
forced onto the pin signals. In the capture phase, the results of this test
data are stored in the capture registers, then shifted out of TDOduring the
shift phase. New test data can then be stored in the update registers
during the update phase.
The EXTESTwaveform diagram in Figure 14–11 resembles the
SAMPLE/PRELOADwaveform diagram, except for the instruction code.
The data shifted out of TDOconsists of the data that was present in the
capture registers after the capture phase. New test data shifted into the
TDIpin appears at the TDOpin after being clocked through the entire
boundary-scan register.
Figure 14–11. EXTEST Shift Data Register Waveforms
TCK
TMS
TDI
TDO
SHIFT_IR
SHIFT_DR
TAP_STATE
EXIT1_IR
SELECT_DR
CAPTURE_DR
EXIT1_DR
After boundary-scan
register data has been
shifted out, data
entered into TDI will
shift out of TDO.
Data stored in
boundary-scan
register is shifted
out of TDO.
UPDATE_IR
UPDATE_DR
Instruction Code
BYPASS Instruction Mode
The BYPASSmode is activated when an instruction code of all 1’s is
loaded in the instruction register. The waveforms in Figure 14–12 show
how scan data passes through a device once the TAP controller is in the
SHIFT_DRstate. In this state, data signals are clocked into the bypass
register from TDIon the rising edge of TCKand out of TDOon the falling
edge of the same clock pulse.
Altera Corporation
February 2007
14–13
Cyclone II Device Handbook, Volume 1
ALTERA [ ALTERA CORPORATION ]
