Chapter 13: IEEE 1149.1 (JTAG) Boundary-Scan Testing for MAX II Devices
IEEE Std. 1149.1 BST Operation Control
13–13
EXTEST
selects data differently than
SAMPLE/PRELOAD. EXTEST
chooses data from
the update registers as the source of the output and output enable signals. Once the
EXTEST
instruction code is entered, the multiplexers select the update register data;
thus, data stored in these registers from a previous
EXTEST
or
SAMPLE/PRELOAD
test
cycle can be forced onto the pin signals. In the capture phase, the results of this test
data are stored in the capture registers and then shifted out of
TDO
during the shift
phase. New test data can then be stored in the update registers during the update
phase.
The waveform diagram in
resembles the
SAMPLE/PRELOAD
waveform
diagram, except that the instruction code for
EXTEST
is different. The data shifted out
of
TDO
consists of the data that was present in the capture registers after the capture
phase. New test data shifted into the
TDI
pin appears at the
TDO
pin after being
clocked through the entire boundary-scan register.
Figure 13–11.
EXTEST Shift Data Register Waveforms
TCK
TMS
TDI
TDO
SHIFT_IR
TAP_STATE
EXIT1_IR
Instruction Code
SELECT_DR_SCAN
Data stored in
UPDATE_IR
CAPTURE_DR
boundary-scan
register is shifted
out of TDO.
After boundry-scan
register data has been
shifted out, data
entered into TDI will
shift out of TDO.
EXIT1_DR
UPDATE_DR
SHIFT_DR
BYPASS Instruction Mode
The
BYPASS
instruction mode is activated with an instruction code made up of only
ones. The waveforms in
show how scan data passes through a device
once the TAP controller is in the
SHIFT_DR
state. In this state, data signals are clocked
into the bypass register from
TDI
on the rising edge of
TCK
and out of
TDO
on the
falling edge of the same clock pulse.
Figure 13–12.
BYPASS Shift Data Register Waveforms
TCK
TMS
TDI
TDO
SHIFT_IR
TAP_STATE
EXIT1_IR
SELECT_DR_SCAN
Bit 1
Bit 2
Bit 1
Bit 3
Bit 2
Bit n
SHIFT_DR
Instruction Code
UPDATE_IR
Data shifted into TDI on
CAPTURE_DR
the rising edge of TCK is
shifted out of TDO on the
falling edge of the same
TCK pulse.
EXIT1_DR
UPDATE_DR
ALTERA [ ALTERA CORPORATION ]
