EP4CE40 datasheet(224/488 Pages) ALTERA

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Chapter 8: Configuration and Remote System Upgrades in Cyclone IV Devices

Configuration

Cyclone IV Device Handbook,

May 2013

Altera Corporation

Volume 1

■

In AP configuration scheme, the only way to re-engage the AP controller is to issue

the ACTIVE_ENGAGE instruction. In this case, asserting the nCONFIG pin does not re-

engage either active controller.

ACTIVE_ENGAGE

The ACTIVE_ENGAGE instruction allows you to re-engage a disengaged active controller.

You can issue this instruction any time during configuration or user mode to re-

engage an already disengaged active controller, as well as trigger reconfiguration of

the Cyclone IV device in the active configuration scheme.

The ACTIVE_ENGAGE instruction functions as the PULSE_NCONFIG instruction when the

device is in the PS or FPP configuration schemes. The nCONFIG pin is disabled when

the ACTIVE_ENGAGE instruction is issued.

1 Altera does not recommend using the ACTIVE_ENGAGE instruction, but it is provided as

a fail-safe instruction for re-engaging the active configuration controller (AS and AP).

Overriding the Internal Oscillator

This feature allows you to override the internal oscillator during the active

configuration scheme. The AS and AP configuration controllers use the internal

oscillator as the clock source. You can change the clock source to CLKUSR through the

JTAG instruction.

The EN_ACTIVE_CLK and DIS_ACTIVE_CLK JTAG instructions toggle on or off whether

or not the active clock is sourced from the CLKUSR pin or the internal configuration

oscillator. To source the active clock from the CLKUSR pin, issue the EN_ACTIVE_CLK

instruction. This causes the CLKUSR pin to become the active clock source. When using

the EN_ACTIVE_CLK instruction, you must enable the internal oscillator for the clock

change to occur. By default, the configuration oscillator is disabled after configuration

and initialization is complete as well as the device has entered user mode.

However, the internal oscillator is enabled in user mode by any of the following

conditions:

■

A reconfiguration event (for example, driving the nCONFIG pin to go low)

■

Remote update is enabled

■

Error detection is enabled

1 When using the EN_ACTIVE_CLK and DIS_ACTIVE_CLK JTAG instructions to override

the internal oscillator, you must clock the CLKUSR pin at two times the expected DCLK

frequency. The CLKUSR pin allows a maximum frequency of 40 MHz (40 MHz DCLK).

Normally, a test instrument uses the CLKUSR pin when it wants to drive its own clock

to control the AS state machine.

To revert the clock source back to the configuration oscillator, issue the

DIS_ACTIVE_CLK

instruction. After you issue the DIS_ACTIVE_CLK instruction, you

must continue to clock the CLKUSR pin for 10 clock cycles. Otherwise, even toggling the

nCONFIG

pin does not revert the clock source and reconfiguration does not occur. A

POR reverts the clock source back to the configuration oscillator. Toggling the nCONFIG

pin or driving the JTAG state machine to reset state does not revert the clock source.

EP4CE40 Datasheet(PDF) 224 Page - Altera Corporation

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