Datasheet

SN54LVTH18646A, SN54LVTH182646A, SN74LVTH18646A, SN74LVTH182646A
3.3-V ABT SCAN TEST DEVICES
WITH 18-BIT TRANSCEIVERS AND REGISTERS
SCBS311D – MARCH 1994 – REVISED JUNE 1997
11
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
data register description
boundary-scan register
The boundary-scan register (BSR) is 52 bits long. It contains one boundary-scan cell (BSC) for each
normal-function input pin, one BSC for each normal-function I/O pin (one single cell for both input data and
output data), and one BSC for each of the internally decoded output-enable signals (1OEA, 2OEA, 1OEB,
2OEB). The BSR is used 1) to store test data that is to be applied 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, BSCs 51–48 are reset to logic 0, 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). Reset values of other BSCs should be considered indeterminate.
When external data is to be captured, the BSCs for signals 1OEA, 2OEA, 1OEB, and 2OEB capture logic values
determined by the following positive-logic equations:
1OEA 1OE
• 1DIR,2OEA 2OE • 2DIR,1OEB 1OE • DIR, 2OEB 2OE • DIR
When data is to be applied externally, these BSCs control the drive state (active or high impedance) of their
respective outputs.
The BSR order of scan is from TDI through bits 51–0 to TDO. Table 1 shows the BSR bits and their associated
device pin signals.
Table 1. Boundary-Scan Register Configuration
BSR BIT
NUMBER
DEVICE
SIGNAL
BSR BIT
NUMBER
DEVICE
SIGNAL
BSR BIT
NUMBER
DEVICE
SIGNAL
51 2OEB 35 2A9-I/O 17 2B9-I/O
50 1OEB 34 2A8-I/O 16 2B8-I/O
49 2OEA 33 2A7-I/O 15 2B7-I/O
48 1OEA 32 2A6-I/O 14 2B6-I/O
47 2DIR 31 2A5-I/O 13 2B5-I/O
46 1DIR 30 2A4-I/O 12 2B4-I/O
45 2OE 29 2A3-I/O 11 2B3-I/O
44 1OE 28 2A2-I/O 10 2B2-I/O
43 2CLKAB 27 2A1-I/O 9 2B1-I/O
42 1CLKAB 26 1A9-I/O 8 1B9-I/O
41 2CLKBA 25 1A8-I/O 7 1B8-I/O
40 1CLKBA 24 1A7-I/O 6 1B7-I/O
39 2SAB 23 1A6-I/O 5 1B6-I/O
38 1SAB 22 1A5-I/O 4 1B5-I/O
37 2SBA 21 1A4-I/O 3 1B4-I/O
36 1SBA 20 1A3-I/O 2 1B3-I/O
–– –– 19 1A2-I/O 1 1B2-I/O
–– –– 18 1A1-I/O 0 1B1-I/O