
SN54ABTH18504A, SN54ABTH182504A, SN74ABTH18504A, SN74ABTH182504A
SCAN TEST DEVICES WITH
20-BIT UNIVERSAL BUS TRANSCEIVERS
SCBS165C – AUGUST 1993 – REVISED JULY 1996
13
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
instruction-register opcode description
The instruction-register opcodes are shown in Table 3. The following descriptions detail the operation of
each instruction.
Table 3. Instruction-Register Opcodes
BINARY CODE
BIT 7
→
BIT 0
MSB
→
LSB
00000000
SCOPE OPCODE
DESCRIPTION
SELECTED
DATA REGISTER
MODE
EXTEST
Boundary scan
Boundary scan
Test
10000001
IDCODE
Identification read
Device identification
Normal
10000010
SAMPLE/PRELOAD
BYPASS
BYPASS
BYPASS
Sample boundary
Boundary scan
Normal
00000011
Bypass scan
Bypass
Normal
10000100
Bypass scan
Bypass
Normal
00000101
Bypass scan
Bypass
Normal
00000110
HIGHZ
Control boundary to high impedance
Bypass
Modified test
10000111
CLAMP
BYPASS
Control boundary to 1/0
Bypass
Test
10001000
Bypass scan
Bypass
Normal
00001001
RUNT
Boundary run test
Bypass
Test
00001010
READBN
Boundary read
Boundary scan
Normal
10001011
READBT
Boundary read
Boundary scan
Test
00001100
CELLTST
Boundary self test
Boundary scan
Normal
10001101
TOPHIP
Boundary toggle outputs
Bypass
Test
10001110
SCANCN
Boundary-control register scan
Boundary control
Normal
00001111
SCANCT
Boundary-control register scan
Boundary control
Test
All others
BYPASS
Bypass scan
Bypass
Normal
Bit 7 is used to maintain even parity in the 8-bit instruction.
The BYPASS instruction is executed in lieu of a SCOPE
instruction that is not supported in the ’ABTH18504A or ’ABTH182504A.
boundary scan
This instruction conforms to the IEEE Standard 1149.1-1990 EXTEST instruction. The BSR is selected in the
scan path. Data appearing at the device input and I/O pins is captured in the associated BSCs. Data that has
been scanned into the I/O BSCs for pins in the output mode is applied to the device I/O pins. Data present at
the device pins, except for output-enables, is passed through the BSCs to the normal on-chip logic. For I/O pins,
the operation of a pin as input or output is determined by the contents of the output-enable BSCs (bits 47–46
of the BSR). When a given output enable is active (logic 0), the associated I/O pins operate in the output mode.
Otherwise, the I/O pins operate in the input mode. The device operates in the test mode.
identification read
This instruction conforms to the IEEE Standard 1149.1-1990 IDCODE instruction. The IDR is selected in the
scan path. The device operates in the normal mode.
sample boundary
This instruction conforms to the IEEE Standard 1149.1-1990 SAMPLE/PRELOAD instruction. The BSR is
selected in the scan path. Data appearing at the device input pins and I/O pins in the input mode is captured
in the associated BSCs, while data appearing at the outputs of the normal on-chip logic is captured in the BSCs
associated with I/O pins in the output mode. The device operates in the normal mode.