Datasheet
SN74ABT18502
SCAN TEST DEVICE
WITH 18-BIT REGISTERED BUS TRANSCEIVER
SCBS753 – FEBRUARY 2002
9
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
data register (DR)
boundary-scan register (BSR)
The BSR is 84 bits long. It contains one BSC for each normal-function input pin and two BSCs for each
normal-function I/O pin (one for input data and one for output data). The BSR is used 1) to store test data that
is to be applied internally to the inputs of the normal on-chip logic and/or externally to the device output pins,
and/or 2) to capture data that appears internally at the outputs of the normal on-chip logic and/or externally at
the device input pins.
The source of data to be captured into the BSR during Capture-DR is determined by the current instruction. The
contents of the BSR can change during Run-Test/Idle as determined by the current instruction. At power up or
in Test-Logic-Reset, the value of each BSC is reset to logic 0 except BSCs 83–80, which are reset to logic 1,
ensuring that these cells, which control A-port and B-port outputs are set to benign values (i.e., if test mode were
invoked, the outputs would be at high impedance state). Rest values of other BSCs should be considered
indeterminate.
The BSR order of scan is from TDI through bits 83–0 to TDO. Table 1 shows the BSR bits and their associated
device pin signals.
Table 1. BSR Configuration
BSR BIT
NUMBER
DEVICE
SIGNAL
BSR BIT
NUMBER
DEVICE
SIGNAL
BSR BIT
NUMBER
DEVICE
SIGNAL
BSR BIT
NUMBER
DEVICE
SIGNAL
BSR BIT
NUMBER
DEVICE
SIGNAL
83 2OEAB 71 2A9-I 53 2A9-O 35 2B9-I 17 2B9-O
82 1OEAB 70 2A8-I 52 2A8-O 34 2B8-I 16 2B8-O
81 2OEBA 69 2A7-I 51 2A7-O 33 2B7-I 15 2B7-O
80 1OEBA 68 2A6-I 50 2A6-O 32 2B6-I 14 2B6-O
79 2CLKAB 67 2A5-I 49 2A5-O 31 2B5-I 13 2B5-O
78 1CLKAB 66 2A4-I 48 2A4-O 30 2B4-I 12 2B4-O
77 2CLKBA 65 2A3-I 47 2A3-O 29 2B3-I 11 2B3-O
76 1CLKBA 64 2A2-I 46 2A2-O 28 2B2-I 10 2B2-O
75 2LEAB 63 2A1-I 45 2A1-O 27 2B1-I 9 2B1-O
74 1LEAB 62 1A9-I 44 1A9-O 26 1B9-I 8 1B9-O
73 2LEBA 61 1A8-I 43 1A8-O 25 1B8-I 7 1B8-O
72 1LEBA 60 1A7-I 42 1A7-O 24 1B7-I 6 1B7-O
–– –– 59 1A6-I 41 1A6-O 23 1B6-I 5 1B6-O
–– –– 58 1A5-I 40 1A5-O 22 1B5-I 4 1B5-O
–– –– 57 1A4-I 39 1A4-O 21 1B4-I 3 1B4-O
–– –– 56 1A3-I 38 1A3-O 20 1B3-I 2 1B3-O
–– –– 55 1A2-I 37 1A2-O 19 1B2-I 1 1B2-O
–– –– 54 1A1-I 36 1A1-O 18 1B1-I 0 1B1-O