EP2C8T144C8N Datasheet, PDF (439/470 Pages) Altera Corporation – Cyclone II Device Handbook, Volume 1

IEEE 1149.1 (JTAG) Boundary-Scan Testing for Cyclone II Devices
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, 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 EXTEST waveform diagram in Figure 14–11 resembles the
SAMPLE/PRELOAD waveform diagram, except for the instruction code.
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 14–11. EXTEST Shift Data Register Waveforms
TCK
TMS
TDI
TDO
SHIFT_IR
TAP_STATE
EXIT1_IR SELECT_DR
Instruction Code
UPDATE_IR CAPTURE_DR
Data stored in
boundary-scan
register is shifted
out of TDO.
SHIFT_DR
After boundary-scan EXIT1_DR
register data has been _{UPDATE_DR}
shifted out, data
entered into TDI will
shift out of TDO.
BYPASS Instruction Mode
The BYPASS mode 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_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.
Altera Corporation
February 2007
14–13
Cyclone II Device Handbook, Volume 1