N S 7 5 2 0 b o o t s t r a p i n i t i a l i z a t i o n

NS7520 bootstrap initialization

Many internal NS7520 features are configured when the RESET pin is asserted. The address bus configures the appropriate control register bits at powerup. (See also "External oscillator mode hardware configuration," beginning on page 51.)

Address bit

Name

Description

 

 

 

 

ADDR[27]

Endian configuration

0

Little Endian configuration

 

 

1

Big Endian configuration

 

 

 

 

ADDR[26]

CPU bootstrap

0

CPU disabled; GEN_BUSER=1

 

 

1

CPU enabled; GEN_BUSER=0

 

 

 

 

ADDR[24:23]

CS0/MMCR[19:18] setting

00

8-bit SRAM, 63 wait-states/b00

 

 

01

32-bit SRAM, 63 wait-states/b01

 

 

10

32-bit SRAM

 

 

11

16-bit SRAM, 63 wait-states/b11

 

 

 

ADDR[19:09]

GEN_ID setting

GEN_ID=A[19:09], Default=’h3ff

 

 

 

ADDR[8:7]

PLL IS setting

IS=A[8:7], Default=’b10

 

 

 

ADDR[6:5]

PLL FS setting

FS=A[6:5], Default=’b00

 

 

 

ADDR[4:0]

PLL ND setting

ND=A[4:0], Default=’b01011

 

 

 

 

Note: The initial operating bus speed must be selected by adding pulldown to the address lines that preset the ND value (ADDR[4:0]).

6 0

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 manual NS7520 bootstrap initialization, Address bit Name Description