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HSSI Null Modem Cable
HSSI Null Modem Cable
The null modem cable (CAB-HNUL=) can connect two routers directly back to back. The null
modem cable is 10-feet (3.048 meters) long. Figure 1-6 shows the null modem cable. The maximum
null modem cable length allowed is 50 feet (15.24 meters). The two routers must be in the same
location and can be two Cisco 7000 series routers, two Cisco 7500 series routers, two Cisco 7200
series routers, two Cisco uBR7200 series routers, or any combination of each. A null modem
connection allows you to verify the operation of the HSSI or to link the routers directly in order to
build a larger node.
Figure 1-6 Null Modem Cable Connectors
The null modem cable uses the same 50-pin connectors as the HSSI cable, but uses the pinouts listed
in Table 1-2. For connection and configuration instructions, refer to Chapter 7, “Cable Installation
and Interface Configuration,” for information about attaching null modem cables.
Table 1-2 HSSI Null Modem Cable Pinouts
Caution
Although the HSSI connector and the HSSI cable are similar to SCSI-II format, they are
not identical. The HSSI cable specification is more restrictive than that for the SCSI-II. If a SCSI-II
cable is used instead of an HSSI cable, proper operation cannot be guaranteed.
Signal Name From Pins Direction To Pins Signal Name
RT (Receive Timing) 2, 27 —> 9, 34 TT (Terminal Timing)
CA (DCE available) 3, 28 —> 8, 33 TA (DTE Available)
RD (Receive Data) 4, 29 —> 11, 36 SD (Send Data)
LC (Loopback C) 5, 30 —> 10, 35 LA (Loopback A)
ST (Send Timing) 6, 31 —> 6, 31 ST (Send Timing)
TA (DTE available) 8, 33 —> 3, 28 CA (DCE Available)
TT (Terminal Timing) 9, 34 —> 2, 27 RT (Receive Timing)
LA (Loopback A) 10, 35 —> 5, 30 LC (Loopback C)
SD (Send Data) 11, 36 —> 4, 29 RD (Receive Data)
GND (Ground) 1, 26,
7, 32,
13, 38,
19, 44,
25, 50
1, 26,
7, 32,
13, 38,
19, 44,
25, 50
GND (Ground)
Loopback (not
connected)
12, 37
12, 37 Loopback (not connected)
Not used 14–18, 20–24,
39–43, 45–49
14–18,20–24,
39–43, 45–49
Not used
H5692