sp304ct Exar Corporation, sp304ct Datasheet - Page 10

• Manufacturer Part Number: sp304ct
• Description: Rs-232/rs-422 Line Drivers/receivers
• Manufacturer: Exar Corporation

86
LOOPBACK
The SP304 has a function called loopback, which is
essentially a chip self-test. However, by connecting
system test loops with the inputs and outputs of the
SP304, a system-level diagnostic can be run on
power-up or on command. The test loops can be
Two -Channel Full Duplex RS-232
ROA
ROA
TIA
ROB
ROB
TIA
TIB
RS-232 LINE DRIVER
RS-232 RECEIVER
RS-232 LINE DRIVER
RS-232 RECEIVER
TIB
RS-232 LINE DRIVER
RS-232 RECEIVER
RS-232 LINE DRIVER
RS-232 RECEIVER
2
1
2
1
2
1
1
2
SELECT A = 0
SELECT B = 0
LB = 0
SP304 CONFIGURATIONS IN LOOPBACK MODE
(ACTIVE)
TOB
TOA
TOB
TOA
RIB
RIA
RIA
RIB
1
2
2
2
1
1
2
1
enabled and disabled allowing both system test and
operation with the same components. A maximum
data rate for loopback of 3kbps is recommended.
Loopback is a pin-programmable function, activated
by a logic low on the LB pin (19). As shown in these
figures, the loopback function internally con-
One-Channel Full Duplex RS-232 &
RS-422 LINE DRIVER
RS-422 RECEIVER
RS-232 LINE DRIVER
RS-232 RECEIVER
One-Channel Full Duplex RS-422
RS-232 LINE DRIVER
RS-232 RECEIVER
TIA
TIA
ROA
ROA
ROB
TIB
1
2
1
1
2
1
SELECT A = 0
SELECT B = 1
LB = 0
(ACTIVE)
TOB
TOA
TOA
TOB
RIB
RIB
RIA
RIA
SIGNAL PROCESSING EXCELLENCE
1
2
1
2
2
1
2
1
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