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Chapter 8: Configuration and Remote System Upgrades in Cyclone IV Devices
Configuration
May 2013
Altera Corporation
■
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.
Summary of Contents for Cyclone IV
Page 10: ...x Chapter Revision Dates Cyclone IV Device Handbook March 2016 Altera Corporation Volume 1...
Page 14: ...I 2 Section I Device Core Cyclone IV Device Handbook March 2016 Altera Corporation Volume 1...
Page 274: ...vi Contents Cyclone IV Device Handbook February 2015 Altera Corporation Volume 2...
Page 440: ...iv Contents Cyclone IV Device Handbook December 2016 Altera Corporation Volume 3...
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