S Y S M o d u l e

 

 

 

 

 

 

 

 

 

 

 

 

Bits

Access

Mnemonic

Reset

Description

 

 

 

 

 

 

 

D08:07

Read

IS

‘b10

Charge pump current

 

 

only

 

 

Sets the PLL’s charge pump current.

 

 

 

 

The IS field defaults to binary ‘b10 when address

 

 

 

 

lines [8:7] are not pulled down on powerup. The

 

 

 

 

IS value is based on the value in the ND field.

 

 

 

 

(ND+1)

IS

 

 

 

 

1–3

‘b00

 

 

 

 

4–7

‘b01

 

 

 

 

8–15

‘b10

 

 

 

 

16–32

‘b11

 

 

 

 

 

 

D06:05

Read

FS

‘b00

Output divider

 

 

only

 

 

Sets the PLL’s output divider.

 

 

 

 

The FS field defaults to ‘b00 when address lines

 

 

 

 

[6:5] are not pulled down on powerup. This is the

 

 

 

 

correct setting for all frequencies and should

 

 

 

 

never be adjusted.

 

 

 

 

 

 

 

D04:00

Read

ND

‘b01011

PLL multiplier

 

 

only

 

 

Sets the PLL’s multiplier, which determines BCLK

 

 

 

 

frequency.

 

BCLK frequency is based on tis formula: BCLK = (crystal/4) (ND+1)

The ND field defaults to ‘b01011 to produce 55MHz (with a 18.432MHz crystal) when address lines A[4:0] are not pulled down on powerup.

Table 21: PLL Settings register bit definition

The next table shows the 32 frequencies that can be produced with an 18.432MHz crystal. A 0 on an address indicates that a 2.7K pulldown resistor must be connected to that address line. The table shows the IS, FS, and ND fields, and the resulting value in the PLL Settings register.

MHz

A[8:7]

IS

A[6:5]

FS

A[4:0]

ND+1

PLL Settings reg

Notes

 

 

 

 

 

 

 

 

 

4.6

01

00

11

00

10100

00001

0x00000000

 

 

 

 

 

 

 

 

9.2

01

00

11

00

10101

00010

0x00000001

 

 

 

 

 

 

 

 

13.8

01

00

11

00

10110

00011

0x00000002

w w w . d i g i . c o m

5 5

Page 69
Image 69
Digi NS7520 Bits Access Mnemonic Reset Description, Output divider, PLL multiplier, MHz A87 A65 A40 ND+1 PLL Settings reg