Altera Cyclone IV - Extest_Pulse; Extest_Train; I;O Voltage Support in a JTAG Chain

Chapter 10: JTAG Boundary-Scan Testing for Cyclone IV Devices 10–5
I/O Voltage Support in a JTAG Chain
December 2013 Altera Corporation Cyclone IV Device Handbook,
Volume 1
EXTEST_PULSE
The instruction code for EXTEST_PULSE is 0010001111. The EXTEST_PULSE instruction
generates three output transitions:
■ Driver drives data on the falling edge of TCK in UPDATE_IR/DR.
■ Driver drives inverted data on the falling edge of TCK after entering the
RUN_TEST/IDLE state.
■ Driver drives data on the falling edge of TCK after leaving the RUN_TEST/IDLE
state.
1 If you use DC-coupling on HSSI signals, you must execute the
EXTEST instruction. If
you use AC-coupling on HSSI signals, you must execute the
EXTEST_PULSE
instruction. AC-coupled and DC-coupled HSSI are only supported in
post-configuration mode.
EXTEST_TRAIN
The instruction code for EXTEST_TRAIN is 0001001111. The EXTEST_TRAIN instruction
behaves the same as the
EXTEST_PULSE instruction with one exception. The output
continues to toggle on the
TCK falling edge as long as the test access port (TAP)
controller is in the RUN_TEST/IDLE state.
1 These two instruction codes are only supported in post-configuration mode for
Cyclone IV GX devices.
1 When you perform JTAG boundary-scan testing before configuration, the
nCONFIG pin
must be held low.
I/O Voltage Support in a JTAG Chain
A Cyclone IV device operating in BST mode uses four required pins: TDI , TDO , TMS ,
and
TCK . The TDO output pin and all JTAG input pins are powered by the V
CCIO
power
supply of I/O Banks (I/O Bank 9 for Cyclone IV GX devices and I/O Bank 1 for
Cyclone IV E devices).
A JTAG chain can contain several different devices. However, you must use caution if
the chain contains devices that have different V
CCIO
levels. The output voltage level of
the
TDO pin must meet the specification of the TDI pin it drives. For example, a device
with a 3.3-V
TDO pin can drive a device with a 5.0-V TDI pin because 3.3 V meets the
minimum TTL-level V
IH
for the 5.0-V TDI pin.
1 For multiple devices in a JTAG chain with the 3.0-V/3.3-V I/O standard, you must
connect a 25- series resistor on a
TDO pin driving a TDI pin.
You can also interface the
TDI and TDO lines of the devices that have different V
CCIO
levels by inserting a level shifter between the devices. If possible, the JTAG chain
should have a device with a higher V
CCIO
level driving a device with an equal or
lower V
CCIO
level. This way, a level shifter may be required only to shift the TDO level
to a level acceptable to the JTAG tester.