Datasheet

SN54ABT8543, SN74ABT8543
SCAN TEST DEVICES WITH
OCTAL REGISTERED BUS TRANSCEIVERS
SCBS120E – AUGUST 1991 – REVISED JULY 1996
16
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
simultaneous PSA and binary count up (PSA/COUNT)
Data appearing at the selected device input pins is compressed into an 8-bit parallel signature in the
shift-register elements of the selected input BSCs on each rising edge of TCK. This data is updated in the
shadow latches of the selected input BSCs and applied to the inputs of the normal on-chip logic. At the same
time, an 8-bit binary count-up pattern is generated in the shift-register elements of the selected output BSCs
on each rising edge of TCK, updated in the shadow latches, and applied to the associated device output pins
on each falling edge of TCK. The shift-register elements of the opposite output BSCs count carries out of the
selected output BSCs, extending the count to 16 bits. Figures 10 and 11 show the 8-bit linear-feedback
shift-register algorithms through which the signature is generated. An initial seed value should be scanned into
the BSR before performing this operation.
=
=
MASKX
A8-I
B8-O
A7-I A6-I A5-I A4-I A3-I A2-I A1-I
B7-O B6-O B5-O B4-O B3-O B2-O B1-O
MSB LSB
Figure 10. 8-Bit PSA/COUNT Configuration (OEA = 0, OEB = 1)
=
=
MASKX
B8-I
A8-O
B7-I B6-I B5-I B4-I B3-I B2-I B1-I
A7-O A6-O A5-O A4-O A3-O A2-O A1-O
MSB LSB
Figure 11. 8-Bit PSA/COUNT Configuration (OEA = 1, OEB = 0)