SP301 Datasheet, PDF (13/18 Pages) Sipex Corporation – RS-232/RS-422 Line Drivers/Receivers

LOOPBACK
Both the SP301 and SP302 have a function called
loopback, which is essentially a chip self-test. How-
ever, by connecting system test loops with the inputs
and outputs of the SP301/302, a system-level diag-
nostic 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 func-
tion, activated by a logic low on the LB pin (19). As
SP301 CONFIGURATIONS IN LOOPBACK MODE
Two -Channel Full Duplex RS-232
One-Channel Full Duplex RS-232 &
One-Channel Full Duplex RS-422
TIA
TOA₁
TIB
RS-232 LINE DRIVERS
RS-232 RECEIVERS
ROA
TOB₁
RIA₁
ROB
RIB₁
SELECT A = 0
SELECT B = 0
LB = 1
TIA
RS-232 LINE DRIVER
RS-232 RECEIVER
ROA
TOA₁
10k
10k _VEE
RIA₁
10k
V_{EE 10k}
TIB
RS-422 LINE DRIVER
RS-422 RECEIVER
ROB
TOB₂
TOB₁
10k
10k _VEE
RIB₁
RIB₂
SELECT A = 0
SELECT B = 1
LB = 0 ^(ACTIVE)
Corporation
SIGNAL PROCESSING EXCELLENCE
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