Axcelerator Family FPGAs
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2 - 107
mode if desired. Please note, if the I/O bank is not disabled, differential I/Os belonging to the I/O bank will
The Axcelerator device will resume normal operation 10
μs after the LP pin is pulled Low.
To further reduce power consumption, the internal charge pump can be bypassed and an external power
supply voltage can be used instead. This saves the internal charge-pump operating current, resulting in
no DC current draw. The Axcelerator family devices have a dedicated "VPUMP" pin that can be used to
access an external charge pump device. In normal chip operation, when using the internal charge pump,
VPUMP should be tied to GND. When the voltage level on VPUMP is set to 3.3V, the internal charge pump
is turned off, and the VPUMP voltage will be used as the charge pump voltage. Adequate voltage
regulation (i.e. high drive, low output impedance, and good decoupling) should be used at VPUMP.
In addition, any PLL in use can be powered down to further reduce power consumption. This can be
done with the PowerDown pin driven Low. Driving this pin High restarts the PLL with the output clock(s)
being stable once lock is restored.
JTAG
Axcelerator offers a JTAG interface that is compliant with the IEEE 1149.1 standard. The user can
employ the JTAG interface for probing a design and performing any JTAG Public Instructions as defined
Interface
The interface consists of four inputs: Test Mode Select (TMS), Test Data In (TDI), Test Clock (TCK), TAP
Controller Reset (TRST), and an output, Test Data Out (TDO). TMS, TDI, and TRST have on-chip pull-up
resistors.
TRST
TRST (Test-Logic Reset) is an active-low, asynchronous reset signal to the TAP controller. The TRST
input can be used to reset the Test Access Port (TAP) Controller to the TRST state. The TAP Controller
can be held at this state permanently by grounding the TRST pin. To hold the JTAG TAP controller in the
TRST state, it is recommended to connect TRST to ground via a 1 k
Ω resistor.
There is an optional internal pull-up resistor available for the TRST input that can be set by the user at
programming. Care should be exercised when using this option in combination with an external tie-off to
ground.
An on-chip power-on-reset (POWRST) circuit is included. POWRST has the same function as "TRST,"
but it only occurs at power-up or during recovery from a VCCA and/or VCCDA voltage drop.
Table 2-103 JTAG Instruction Code
Instruction (IR4:IR0)
Binary Code
Extest
00000
Preload / Sample
00001
Intest
00010
USERCODE
00011
IDCODE
00100
HIGHZ
01110
CLAMP
01111
Diagnostic
10000
Reserved
All others
Bypass
11111