Intel 386 User Manual page 600

D.32 IR
Instruction Register
IR
Bit Bit
Number Mnemonic
3–0 INST3:0
3
Instruction opcode. At reset (using TRST#, or after 5 TCK cycles with
TMS held low), this field is loaded with 0010, the opcode for the IDCODE
instruction. Instructions are shifted into this field serially through the TDI
pin. (Table 18-4 lists the valid instruction opcodes.)
SYSTEM REGISTER QUICK REFERENCE
Reset State
(Using TRST#): 02H
INST3 INST2 INST1
Function
0
INST0
D-35