SP304 Datasheet, PDF (10/12 Pages) Sipex Corporation – RS-232/RS-422 Line Drivers/Receivers

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
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-
SP304 CONFIGURATIONS IN LOOPBACK MODE
Two -Channel Full Duplex RS-232
TIA₁
TOA₁
One-Channel Full Duplex RS-232 &
One-Channel Full Duplex RS-422
RS-232 LINE DRIVER
RS-232 RECEIVER
ROA₁
TIA₂
RIA₁
TOA₂
RS-232 LINE DRIVER
RS-232 RECEIVER
ROA₂
TIB₁
RIA₂
TOB₁
TIB₁
RS-422 LINE DRIVER
RS-422 RECEIVER
ROB₁
TIA₁
TOB₂
TOB₁
RIB₁
RIB₂
TOA₁
RS-232 LINE DRIVER
RS-232 RECEIVER
ROB₁
TIB₂
RIB₁
TOB₂
RS-232 LINE DRIVER
RS-232 RECEIVER
ROB₂
RIB₂
RS-232 LINE DRIVER
RS-232 RECEIVER
ROA₁
TIA₂
RS-232 LINE DRIVER
RS-232 RECEIVER
ROA₂
RIA₁
TOA₂
RIA₂
SELECT A = 0
SELECT B = 0
LB = 0 ^(ACTIVE)
SELECT A = 0
SELECT B = 1
LB = 0 ^(ACTIVE)
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SIGNAL PROCESSING EXCELLENCE