SWAN Concentrator Installation and Support Guide

Cable Specifications
SWAN Concentrator Installation and Support Guide—429391-006
B-21
Interface Select (ISEL Code)
The four-bit ISEL value is %b0000.
Interface Select (ISEL Code)
SWAN uses the ISEL code to determine which type of cable or loopback connector is
installed in a WAN port (if any). Each CLIP can read this 4-bit code. Each of the four
bits has a pullup resistor on it, so unless pulled low by the connector, the bit is high. In
the connector housing itself, wires short some of the bits to ground. Each connector
has a unique code as shown in Table B-12.
Three bits are needed to code six connector configurations; the fourth bit, ISEL0, is an
even parity used to confirm that the connector is properly seated. The seating is done
by using four corner pins on the connector. The labels RT, RB, LT, and LB correspond
to the right top, right bottom, left top, and left bottom as you face the cable connector.
There is at least one zero on each of the right and left sides for all codes.
Since the loopback connector is a special case because many pins are shared by the
different interfaces, a method of selecting which drivers to enable is required.
TX_LOOP SEL bits select which drivers to enable when the loopback connector is on.
When the CLIP PAL detects that the loopback connector is in place, it reads the
TX_LOOP_SEL bits and determines which ISEL_CODE to generate. The ISEL_CODE
bits driven to the WAN PAL determine which interface drivers and receivers get
enabled. The QUICC writes the TX_LOOP_SEL bits.
Table B-12. ISEL Decoding
Interface
ISEL3
RT
17
ISEL2
RB
50
ISEL1
LT
1
ISELO
LB
34 TX_LOOP_SEL ISEL_CODE
RS-23210 01 XX 100
RS-44910 10 XX 101
X.21 01 01 XX 010
V.35 01 10 XX 011
Loopback
(RS-232)
00 00 00
Loopback
(RS-449)
00 00 01
Loopback
(X.21)
00 00 10
Loopback
(V.35)
00 00 11
No
connector
11 11 xx 111