EP4CE30F29C7N Datasheet, PDF (224/488 Pages) Altera Corporation – Cyclone IV Device Handbook, Volume 1

8–60
Chapter 8: Configuration and Remote System Upgrades in Cyclone IV Devices
Configuration
■ 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.
Cyclone IV Device Handbook,
Volume 1
May 2013 Altera Corporation