Internal Loopback through the NIC: Matching Physical
Address
Loopback Path
TCR
RCR
TSR
RSR
ISR
Mode 1 (NIC)
02H
00H
51H
02H
06H
TSR:
Before transmission of the loopback packet, Carrier
Sense and Collision inputs are monitored (as re-
quired by CSMA/CD protocol). Once the NIC gains
access to the network for transmission, the Carrier
Sense and Collision Detect inputs are ignored.
Thus, the Carrier Sense Lost and CD Heartbeat bits
are always set in the Transmit Status Register.
RSR:
CRC errors should be seen in both the Receive
Status Register and the Interrupt Status Register for
an address matching packet.
ISR:
Only the Packet Transmitted and Receive Error bits
in the Interrupt Status Register are set; the Packet
Received bit is set only if status is written to memo-
ry. In loopback this action does not occur, hence
the Packet Received bit remains 0 for all loopback
modes.
Internal Loopback through the NIC : Non-Matching
Physical Address
Loopback Path
TCR
RCR
TSR
RSR
ISR
Mode 1 (NIC)
02H
00H
51H
01H
02H
TSR:
Before transmission of the loopback packet, Carrier
Sense and Collision inputs are monitored (as re-
quired by CSMA/CD protocol). Once the NIC gains
access to the network for transmission, the Carrier
Sense and Collision Detect inputs are ignored.
Thus, the Carrier Sense Lost and CD Heartbeat bits
are always set in the Transmit Status Register.
RSR:
CRC errors should not be detected for a non-
matching physical address.
ISR:
Only the Packet Transmitted bit in the Interrupt
Status Register is set. The packet received bit is set
only if status is written to memory. In loopback this
action does not occur, hence the Packet Received
bit remains 0 for all loopback modes.
7.0 COMMON LOOPBACK CONDITIONS AND
CORRESPONDING RESULTS
This section identifies some common variations in the loop-
back results from Section 6.0 which occur when the loop-
back tests or hardware are not configured properly.
7.1 Group I Loopback
If the coax cable is not terminated, the results will differ from
those listed in Section 6.1 as follows:
Loopback Path
TCR
RCR
TSR
RSR
ISR
Mode 3 (CTI)
06H
1FH
0CH
02H
08H
If the coax cable is disconnected, the results will differ from
those listed in Section 6.1 as follows:
Loopback Path
TCR
RCR
TSR
RSR
ISR
Mode 1 (NIC)
02H
1FH
40H
02H
00H
Mode 2 (SNI)
04H
1FH
40H
02H
00H
Mode 3 (CTI)
06H
1FH
00H
82H
00H
If the twisted pair cable is not connected and good link is
enabled, the results will differ from those listed in Section
6.1 as follows:
Loopback Path
TCR
RCR
TSR
RSR
ISR
Mode 2 (SNI)
04H
1FH
51H
02H
02H
Mode 3 (TPI)
06H
1FH
51H
02H
02H
If the twisted pair cable is not connected, and good link is
disabled, the results do not differ from those listed in Sec-
tion 6.1.
If the packet has a non-matching physical address and pro-
miscuous physical mode is not chosen in the Receive Con-
figuration Register, the results will differ from those listed in
6.1 as follows:
Loopback Path
TCR
RCR
TSR
RSR
ISR
Mode 1 (NIC)
02H
00H
51H
01H
02H
Mode 2 (SNI)
04H
00H
41H
01H
02H
Mode 3 (TPI or CTI)
06H
00H
01H
01H
02H
7.2 Group II Loopback
If the coax cable is not terminated, the results will differ from
those listed in Section 6.2 as follows:
Loopback Path
TCR
RCR
TSR
RSR
ISR
Mode 3 (CTI)
07H
1FH
0CH
01H
08H
If the coax cable is disconnected, the results will differ from
those listed in Section 6.2 as follows:
Loopback Path
TCR
RCR
TSR
RSR
ISR
Mode 1 (NIC)
03H
1FH
40H
01H
00H
Mode 2 (SNI)
05H
1FH
40H
01H
00H
Mode 3 (CTI)
07H
1FH
00H
81H
00H
If the twisted pair cable is not connected and good link is
enabled, the results will differ from those listed in Section
6.2 as follows:
Loopback Path
TCR
RCR
TSR
RSR
ISR
Mode 2 (SNI)
05H
1FH
51H
01H
02H
Mode 3 (TPI)
07H
1FH
51H
01H
02H
If the twisted pair cable is not connected, and good link is
disabled, the results do not differ from those listed in Sec-
tion 6.2.
7.3 Group III Loopback
If the coax cable is not terminated, the results do not differ
from those listed in Section 6.3.
If the coax cable is disconnected, the results will differ from
those listed in Section 6.3 as follows:
Packet Contents
TCR
RCR
TSR
RSR
ISR
Matching Physical
02H
00H
40H
01H
00H
Address
Non-Matching
02H
00H
40H
01H
00H
Physical Address
If the twisted pair cable is not connected, regardless of
good link pin’s state, the results do not differ from those
listed in Section 6.3.
7
