EP3C40F324C7N Datasheet, PDF (269/274 Pages) Altera Corporation – Chapter Revision Dates

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
■ 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