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

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