Chapter 12: IEEE 1149.1 (JTAG) Boundary-Scan Testing for the Cyclone III Device Family
I/O Voltage Support in a JTAG Chain
12–5
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Only the three mandatory JTAG 1149.1 JTAG instructions (BYPASS,
SAMPLE/PRELOAD, EXTEST)
and the
FACTORY
private instruction are supported from
the JTAG pins upon power up. The
FACTORY
instruction (instruction code:
10 1000 0001)
must be issued before the device starts loading the core
configuration data to enable access to all other JTAG instructions. This instruction
also clears the device configuration data and AES volatile key.
IDCODE
instruction is not supported upon power-up, prior to issuing the
FACTORY
instruction. However, it is the default instruction when the TAP controller is in the
reset state. Without loading any instructions, you can go to the
Shift_DR
state and
shift out the JTAG Device ID.
IDCODE, CONFIG_IO, ACTIVE_DISENGAGE, HIGHZ, CLAMP, USERCODE
and
PULSE_NCONFIG
instructions are supported, provided that the
FACTORY
instruction is executed.
■
■
I/O Voltage Support in a JTAG Chain
A JTAG chain can contain several different devices. However, you must be cautious if
the chain contains devices that have different V
CCIO
levels. The output voltage level of
the
TDO
pin must meet the specifications of the
TDI
pin it drives. For Cyclone III device
family, the
TDO
pin is powered by the V
CCIO
power supply. Because the V
CCIO
supply is
3.3 V, the
TDO
pin drives out 3.3 V.
Devices can interface with each other although they might have different V
CCIO
levels.
For example, a device with a 3.3-V
TDO
pin can drive to 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. JTAG pins on
Cyclone III device family can support the input levels of V
CCIO
of bank 1A.
1
For multiple devices in a JTAG chain with 3.0-V or 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 must
be built in such a way that a device with a higher V
CCIO
level drives to 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.
December 2011
Altera Corporation
Cyclone III Device Handbook
Volume 1
ALTERA [ ALTERA CORPORATION ]
