From tomj@fido.wps.com Sun Feb 20 21:47:14 1994
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Date: Sun, 20 Feb 94 21:48:58 -0800
From: tomj@wps.com (Tom Jennings)
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To: tomj@tlg.org
Status: OR

Telco 56K leased-line electrical characteristics
Tom Jennings
20 Feb 93

>From information gathered from a Pacific Bell installer, Bell DDS Tech.
Ref., John Harkin and Tim Pozar.


                      Zr
	Rx	0---/////---0		telco to DSU, RJ-48 pins 7, 8
					(has 28KHz clock from telco)
		^	    ^
		|(-)	    |(-)
		|	    |
	       48v         48v
		|	    |
		|	    |
		v(+)	    v(+)

	Tx	0---/////---0		DSU to telco, RJ-48 pins 1,2
                      Zt		
		|	    |
		V	    V
	     ground      ground


Characterising:

Zr and Zt depend on line length; Nominal is 135 ohms.  Just measure
from Tip to Ring on a pair.  There is no battery Tip/Ring on pairs.

There is 48v battery from Rx to Tx pairs. Negative is on the Rx
(telco view). Check tip to tip, and also tip to ring -- thereby
checking for one open conductor.

The clock is 56K Nyquist frequency 28KHz.

Reversing the Rx/Tx pairs causes the LL light to light.

If battery is correct, but you hear clock on the wrong pair, and/or
it acts as if the Rx/Tx pairs are reverse (as above), the telco
might have left "the latch" flipped. Duh. I guess it's some sort
of test-board latch, which reverses the Rx/Tx clock feed, and closes
("latches") a "relay" within the DSU to force Link Loop.


--- RJ-48 WIRING GUIDE


	        	RJ-48S          RJ-48C/RJ-48X
	1=BL    	R1              R
	2=OR    	T1              T
	3=BK
	4=R     	                R1
	5=G     	                T1
	6=Y
	7=BR    	T
	8=SL    	R


	FOR RJ48S 1=R1 2=T1 7=T 8=R
	FOR RJ48C/X 1=R 2=T 4=R1 5=T1

	NOTE: R=RING T=TIP
	NOTE: RJ-48X shorts Rx/Tx when no plug inserted

BAT DSU: RJ-48S		TYLINK CSU/DSU: RJ-48C