MYSON

TECHNOLOGY

MTD492

MTD492 Revision 3.5 01/07/1997

2/8

1.0 CONNECTION DIAGRAM

MTD492N

16 PIN PDIP

MTD492V

28 PIN PLCC

CD+

CD-

RX+

VEE

VEE

RX-

TX+

TX-

CDS

TX0

RXI

VEE

RR-

RR+

GND

HBE

VEE

VEE

VEE

VEE

VEE(NC)

VEE(NC)

VEE(NC)

VEE(NC)

VEE

VEE

VEE

VEE

VEE(NC)

RR-

1

2

3

4

5

6

7

8

24

23

22

21

20

19

18

17

2.0 PIN DESCRIPTIONS

Name

I/O

PDIP

Pin#

PLCC

Pin#

Description

TX+,TX-

I

7,8

13,14 Transmission Data Input. A balanced differential line receiver which

receives inputs from the off-chip Manchester Code Converter(MCC) to

the Transmitter. The common mode voltage on TX+ is set internally .

HBE

I

9

15

Heartbeat Enabler. The CD heartbeat test is enabled when HBE is

connected to Ground and disabled when HBE is connected to VEE.

This pin is internally biased at 0.5 VEE. Test mode is enabled if this

pin is left floating or biased in the range of -3.5V to -5.5V. Jabber is

disabled in test mode. Exiting the jabber disable mode requires at

least jabber reset time.

RR+,RR-

I

11,12

18,19 External Resistor. A 1k

Ω/1% resistor should be connected across

these pins to correctly set internal operating currents. RR+ is

internally shorted to GND.

RXI

I

14

26

Network Receiving Input. Should be connected to the COAX center

conductor. Signals meeting receiver squelch limits are recovered and

output on RX+. RXI also detects the collision voltage level.

CDS

I

16

1

Collision Detection Sense. Connects directly to the COAX

shield, providing a reference for the collision detection voltage

level for reception-mode detection. An external bias network can be

used to shift the detection threshold for transmission-detection mode.

CD+,CD-

O

1,2

2,3

Collision Output. A balanced differential line driver drives this

output pair from the collision detection circuitry. A 10MHz signal from

the internal oscillator is transferred to these outputs in the event of

collision, excessive transmission (jabber), or during heartbeat

condition. These outputs are open sources, and pull-down resistors of

510

Ω to VEE are required. To minimize power dissipation, both open

source outputs are disabled during idle condition, allowing the

common mode on the pull-down resistors to be pulled to VEE.