SN54LVT18502

3.3-V ABT SCAN TEST DEVICE

WITH 18-BIT UNIVERSAL BUS TRANSCEIVERS

SCBS669 – JULY 1996

10

POST OFFICE BOX 655303

boundary-control register

The boundary-control register (BCR) is three bits long. The BCR is used in the context of the boundary-run test

(RUNT) instruction to implement additional test operations not included in the basic SCOPE

™ instruction set.

Such operations include PRPG, PSA, and binary count up (COUNT). Table 4 shows the test operations that

are decoded by the BCR.

During Capture-DR, the contents of the BCR are not changed. At power up or in Test-Logic-Reset, the BCR is

reset to the binary value 010, which selects the PSA test operation. The BCR order of scan is shown in Figure 3.

Bit 0

(LSB)

TDO

TDI

Bit 1

Bit 2

(MSB)

Figure 3. Boundary-Control Register Order of Scan

bypass register

The bypass register is a 1-bit scan path that can be selected to shorten the length of the system scan path,

reducing the number of bits per test pattern that must be applied to complete a test operation. During

Capture-DR, the bypass register captures a logic 0. The bypass register order of scan is shown in Figure 4.

Bit 0

TDO

TDI

Figure 4. Bypass Register Order of Scan