S i g n a l d e s c r i p t i o n

Signal description

The system control signals determine the basic operation of the chip:

Signal mnemonic

Signal name

Description

 

 

 

{XTALA1, XTALA2}

Clock source

Operate in one of two ways:

 

 

The signals are affixed with a 10-20

 

 

MHz parallel mode quartz crystal or

 

 

crystal oscillator and the appropriate

 

 

components per the component

 

 

manufacturer.

 

 

XTALA1 is driven with a clock signal

 

 

and XTALA2 is left open.

 

 

 

{PLLVDD, PLLVSS}

PLL power

Provide an isolated power supply for the

 

 

PLL.

 

 

 

RESET_

Chip reset

Active low signal asserted to initiate a

 

 

hardware reset of the chip.

 

 

 

{TDI, TDO, TNS,

JTAG interface

Provide a JTAG interface for the chip.

TRST_, TCK}

 

This interface is used for both boundary

 

 

scan and ICE control of the internal

 

 

processor.

 

 

 

{PLLTEST_, BISTEN_,

Chip mode

Encoded to determine the chip mode.

SCANEN_}

 

 

 

 

 

JTAG support

The NS7520 provides full support for 1149.1 JTAG boundary scan testing. All NS7520 pins can be controlled using the JTAG interface port. The JTAG interface provides access to the ARM7TDMI debug module when the appropriate combination of PLLTST_, BISTEN_, and SCANEN_ are selected (see "External oscillator mode hardware configuration," beginning on page 51).

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N S 7 5 2 0 H a r d w a r e R e f e r e n c e , R e v . D 0 3 / 2 0 0 6

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Digi NS7520 manual Signal description, Jtag support, Signal mnemonic Signal name Description