EP4CE40 datasheet(261/488 Pages) ALTERA

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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 VCCIO 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 VCCIO 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 VIH 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-

Ω 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

should have a device with a higher VCCIO level driving 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.

EP4CE40 Datasheet(PDF) 261 Page - Altera Corporation

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