Datasheet
SN74ABT18502
SCAN TEST DEVICE
WITH 18-BIT REGISTERED BUS TRANSCEIVER
SCBS753 – FEBRUARY 2002
10
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
boundary-control register (BCR)
The BCR is 21 bits long. The BCR is used in the context of the RUNT instruction to implement additional test
operations not included in the basic SCOPE instruction set. Such operations include PRPG, PSA with input
masking, and binary count up (COUNT). Table 5 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 000000000000000000010, which selects the PSA test operation with no input masking.
The BCR order of scan is from TDI through bits 20–0 to TDO. Table 2 shows the BCR bits and their associated
test control signals.
Table 2. BCR Configuration
BCR BIT
NUMBER
TEST
CONTROL
SIGNAL
BCR BIT
NUMBER
TEST
CONTROL
SIGNAL
BCR BIT
NUMBER
TEST
CONTROL
SIGNAL
20 MASK2.9 11 MASK1.9 2 OPCODE2
19 MASK2.8 10 MASK1.8 1 OPCODE1
18 MASK2.7 9 MASK1.7 0 OPCODE0
17 MASK2.6 8 MASK1.6 –– ––
16 MASK2.5 7 MASK1.5 –– ––
15 MASK2.4 6 MASK1.4 –– ––
14 MASK2.3 5 MASK1.3 –– ––
13 MASK2.2 4 MASK1.2 –– ––
12 MASK2.1 3 MASK1.1 –– ––
bypass register
The bypass register is a 1-bit scan path that can be selected to shorten the length of the system scan path,
thereby 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 3.
Bit 0
TDOTDI
Figure 3. Bypass Register Order of Scan
device identification register (IDR)
The device IDR is 32 bits long. It can be selected and read to identify the manufacturer, part number, and version
of this device.
During Capture-DR, the binary value 00000000000000000110000000101111 (0000602F, hex) is captured in
the device IDR to identify this device as the TI SN74ABT18502, version 0. The device IDR order of scan is from
TDO through bits 31–0 to TDO. Table 3 shows the device IDR bits and their significance.