CDPCLK4 datasheet(269/274 Pages) ALTERA

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Chapter 12: IEEE 1149.1 (JTAG) Boundary-Scan Testing for the Cyclone III Device Family

12–5

I/O Voltage Support in a JTAG Chain

December 2011

Altera Corporation

Cyclone III Device Handbook

Volume 1

■

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 VCCIO 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 VCCIO power supply. Because the VCCIO supply is

3.3 V, the TDO pin drives out 3.3 V.

Devices can interface with each other although they might have different VCCIO 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 VIH for the 5.0-V TDI pin. JTAG pins on

Cyclone III device family can support the input levels of VCCIO 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 VCCIO

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 VCCIO level drives to a device with

an equal or lower VCCIO level. This way, a level shifter may be required only to shift

the TDO level to a level acceptable to the JTAG tester.

CDPCLK4 Scheda tecnica(PDF) 269 Page - Altera Corporation