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Modular Jacks and Cords

Introduction

Modular jacks typically are manufactured in four styles. Eight position, 8 position nonkeyed, 6 position and MMJ (modified modular jack). DEC introduced the MMJ and DEC hardware as its predominant application.

Ethernet 10BaseT

10BaseT wiring specifies an 8 position jack using two pairs. These two pairs 2 & 3 of AT&T and TIA schemes.

IBM Token Ring

Token Ring usually uses an 8 position jack. The wiring scheme is compatible with TIA, AT&T and USOC wiring schemes because it uses the two center pairs.

USOC

The USOC wiring scheme has four versions supporting 1, 2, 3, and 4 pair systems. Pair1 is on the two center contacts, pair 2 is on the next two contacts out and so forth. This scheme is popular because a six position plug configured with 1, 2, or 3 pairs can be inserted into an 8 position jack and maintain pair continuity. Note that pins 1 and 8 in the 8 position jack may be damaged by the insertion of a 6 position plug Degraded transmissions quality has been reported by some users of the USOC wiring scheme.

EIA/TIA and AT&T

EIA/TIA-568 has adopted the EIA/TIA and AT&T wiring schemes. They are similar, bit pairs 2 and 3 are reversed. The TIA scheme is popular because it is compatible with 1 or 2 pair USOC systems. Both schemes will support ISDN applications. Many Category 5 installations are using 568A.

"RJ" Registered Jack

Modular jacks should be referred to by their position count:;;8 position keyed, 6 position, 6 position modified (or MMJ). The RJ designations actually refer to specfic wiring configurations called Universal Service Ordering Services Codes (USOC). The RJ designation means "registered jack". Each of the 8 position jacks and the 6 position jacks can be wired as an RJ11C (1 pair), RJ14C (2 pair), or RJ25C (3 pair). The 8 position jacks can be wired as RJ4555, RJ45S and RJ47s.

EIA RS232 Interface Connector Pin Assignment

PIN

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

Name

FG

TD

RD

RTS

CTS

DSR

SG

DCD

+V

-V

QM

(S)DCD

S CTS

(S) TD

TC

(S) RD

RC

(S) RTS

DTR

SQ

RI

(TC)

To DTE

To DCE

Function

Frame Ground

Transmitted Data

Received Data

Request To Send

Clear To Send

Data Set Ready

Signal Ground

Data Carrier Detect

Positive DC Test Voltage

Negative DC Test Voltage

Equalizer Mode

Sec. Received Data

Receiver Clock

Sec. Transmitted Data

Transmitter Clock

Sec. Received Data

Receiver Clock

Unassigned

Sec. Request To Send

Data Terminal Ready

Signal Quality Detect

Ring Indicator

Data Rate Selector

External Transmitter Clock

Unassigned

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