
SN54LVTH18504A, SN54LVTH182504A, SN74LVTH18504A, SN74LVTH182504A
3.3-V ABT SCAN TEST DEVICES
WITH 20-BIT UNIVERSAL BUS TRANSCEIVERS
SCBS667B – JULY 1996 – REVISED JUNE 1997
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
SCOPE OPCODE
DESCRIPTION
SELECTED
DATA REGISTER
MODE
00000000
EXTEST
Boundary scan
Test
10000001
IDCODE
Identification read
Device identification
Normal
10000010
SAMPLE/PRELOAD
Sample boundary
Boundary scan
Normal
00000011
BYPASS
Bypass scan
Bypass
Normal
10000100
BYPASS
Bypass scan
Bypass
Normal
00000101
BYPASS
Bypass scan
Bypass
Normal
00000110
HIGHZ
Control boundary to high impedance
Bypass
Modified test
10000111
CLAMP
Control boundary to 1/0
Bypass
Test
10001000
BYPASS
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 ’LVTH18504A or ’LVTH182504A.
boundary scan
This instruction conforms to the IEEE Std 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 Std 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 Std 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.