FX579 datasheet(4/23 Pages) CMLMICRO

4 / 23 page

Half Duplex GMSK Modem

FX579

D/579/4

1.3

Signal List

Package

Signal

Description

Pin No.

Name

Type

XTALN

O/P

The output of the on-chip oscillator.

XTAL/CLK

I/P

The input to the on-chip oscillator for an external

Xtal circuit or clock.

CLKDIVA

I/P

) Two logic level inputs that control the internal

CLKDIVB

I/P

) clock divider and hence the transmit and

) receive data rate (See Table 1).

ACQUIRE

I/P

A logic "1" applied to this input will set the Rx

level measurement and Rx clock extraction

circuitry to 'acquire' mode.

VBIAS

O/P

The internal circuitry bias line, held at ½ VDD,

this pin must be decoupled to VSS by a capacitor

mounted close to the pin.

RXIN

I/P

The Rx signal input from the radio's discriminator

via suitable signal and dc level adjustment. In

Rx this pin is internally held at

½ VDD.

VSS

Power

Negative supply rail. Signal ground.

TXOP

O/P

The Tx signal output. This signal should be

applied to an external RC before being applied to

the radio modulator.

I/P

A logic level input to select the modem 'BT' (the

ratio of the Tx filter -3dB frequency to the bit

rate). A logic "1" sets the modem to a BT of 0.5,

a logic "0" to a BT of 0.3.

DOC1

DOC2

O/P

Two pins used by the modem's Rx level

measurement circuitry. A capacitor should be

connected from each pin to VSS.

TXRXN

I/P

A logic level applied to this pin determines

whether the modem operates in Tx or Rx mode.

A logic "1" sets Tx mode. A logic "0" sets Rx

mode.

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