modular jacks and cords, Ethernet 10BaseT, IBM Token Ring

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.

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

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.

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-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.

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