CY22801

Document Number: 001-15571 Rev. *H

Page 5 of 25

Multifunction Pins

There are three pins [1] with multiple functions either as control

pins or as output pins. The following are the acronyms used for

the different control function pins:

one of the programmed clock frequencies for clock output. All

of three multifunction pins support this functionality. Any of

these pins can also be configured as Spread spectrum ON

(SSON) pin. If SSON = 1, clock output has programmed

spread; if SSON = 0, clock output does not have spread.

tristated and the device enters in the low-power state

this pin controls the output frequency of oscillator

(SDAT): These pins are for serial interface and are compatible

Each of these three multi-function pins supports selected

functions mentioned in Table 1. One of the supported functions

can be programmed on the pin at a time.

Frequency Calculation and Register

Definitions

The CY22801 is an extremely flexible clock generator with four

basic variables that are used to determine the final output

frequency. They are the input reference frequency (REF), the

internally calculated P and Q dividers, and the post divider, which

can be a fixed or calculated value. There are three formulas to

determine the final output frequency of a CY22801 based

design:

The basic PLL block diagram is shown in Figure 4. Each of the

three clock outputs on the CY22801 has a total of seven output

options available to it. There are six post divider options

available: /2 (two of these), /3, /4, /DIV1N and /DIV2N. DIV1N

and DIV2N are independently calculated and are applied to

individual output groups. The post divider options can be applied

to the calculated VCO frequency ((REF × P) / Q) or to the REF

directly.

In addition to the six post divider output options, the seventh

option bypasses the PLL and passes the REF directly to the

crosspoint switch matrix.

Table 1. Multi Function Pin Options

Pin#

Pin Name

OE

PD# VCXO FS

CLK

OUTPUT

3

SDAT / FS0 /

VCXO / OE /

PD#

YY

Y[2]

Y[3]

N[4]

SDAT[2]

5

CLKB / FS1 /

SCLK

NN

N

Y

Y

SCLK

7CLKC / FS2

N

N

N

Y

Y[5]

N

Table 2. Possible Combinations for Multifunction Pins

Possible Combinations

Pin#3

Pin#5

Pin#7

A

FS0

CLKB

CLKC

B

FS0

CLKB

FS2

C

FS0

FS1

FS2

D

OE / PD#

CLKB

CLKC

E

OE / PD#

FS1

CLKC

F

OE / PD#

FS1

FS2

G

SDAT

SCLK

CLKC

H

VCXO

CLKB

CLKC

Notes

1. There are Weak Pull up resistors (approximately 100 k

) on all Multifunctional pins.

2. VCXO and SSON functions as well as VCXO and Serial Interface functions are not compatible.

3. ‘Y’ means pin supports this function.

4. ‘N’ means pin does not support this function.

5. Do not use this pin as Reference Clock Output.