Chapter 13: IEEE 1149.1 (JTAG) Boundary-Scan Testing for MAX II Devices
13–11
IEEE Std. 1149.1 BST Operation Control
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 TDOpin. New test data can simultaneously be
shifted into TDIand 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 EXTESTinstruction mode.
Refer to “EXTEST Instruction Mode” on page 13–11 for more information.
Figure 13–9 shows the SAMPLE/PRELOADwaveforms. The SAMPLE/PRELOAD
instruction code is shifted in through the TDIpin. The TAP controller advances to the
CAPTURE_DRstate and then to the SHIFT_DRstate, where it remains if TMSis held
low. The data shifted out of the TDOpin consists 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 13–9 shows that the test data that shifted into TDIdoes not appear at the TDO
pin until after the capture register data that is shifted out. If TMSis held high on two
consecutive TCKclock cycles, the TAP controller advances to the UPDATE_DRstate for
the update phase.
If the device output enable feature is enabled but the DEV_OEpin is not asserted
during boundary-scan testing, the OE boundary-scan registers of the boundary-scan
cells capture data from the core of the device during SAMPLE/PRELOAD. These values
are not high impedance, although the I/O pins are tri-stated.
Figure 13–9. SAMPLE/PRELOAD Shift Data Register Waveforms
TCK
TMS
TDI
TDO
SHIFT_IR
TAP_STATE
SHIFT_DR
EXIT1_IR
UPDATE_IR
EXIT1_DR
SELECT_DR_SCAN
After boundry-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.
Instruction Code
UPDATE_DR
CAPTURE_DR
EXTEST Instruction Mode
The EXTESTinstruction mode is used primarily to check external pin connections
between devices. Unlike the SAMPLE/PRELOADmode, EXTESTallows 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.
Figure 13–10 shows the capture, shift, and update phases of the EXTESTmode.
© October 2008 Altera Corporation
MAX II Device Handbook
ALTERA [ ALTERA CORPORATION ]
