IDT EJTAG System
EJTAG Test Access Port
79RC32438 User Reference Manual
20 - 58
November 4, 2002
Notes
Instruction Register and Special Instructions
The Instruction register controls selection of accessed data register(s), and controls the setting and
clearing of the EJTAGBOOT indication. The Instruction register is five or more bits wide when used with
EJTAG. Table 20.41 shows the allocation of the TAP instruction.
The instructions IDCODE, IMPCODE, ADDRESS, DATA, CONTROL, and BYPASS select a single data
register, as indicated in the table. The unused instructions reserved for EJTAG select the Bypass register.
The ALL, EJTAGBOOT, NORMALBOOT, and FASTDATA instructions are described in the following
subsections. The instructions that are related to trace registers in the trace control block (TCB) are
described in the Trace Control Block Specification document. Any EJTAGBOOT indication is cleared at
power-up either by a low value on the JTAG_TRST_N or by a power-up reset circuit, and the Instruction
register is loaded with the IDCODE instruction.
ALL Instruction
The Address, Data, and EJTAG Control data registers are selected at once with the ALL instruction, as
shown in Figure 20.26.
Code
Instruction
Function
All 0’s
(Free for other use)
Free for other use, such as JTAG boundary scan
0x01
IDCODE
Selects Device Identification (ID) register
0x02
(Free for other use)
Free for other use, such as JTAG boundary scan
0x03
IMPCODE
Selects Implementation register
0x04 — 0x07
(Free for other use)
Free for other use, such as JTAG boundary scan
0x08
ADDRESS
Selects Address register
0x09
DATA
Selects Data register
0x0A
CONTROL
Selects EJTAG Control register
0x0B
ALL
Selects the Address, Data and EJTAG Control registers
0x0C
EJTAGBOOT
Makes the processor take a debug exception after reset
0x0D
NORMALBOOT
Makes the processor execute the reset handler after
reset
0x0E
FASTDATA
Selects the Data and Fastdata registers
0x0F
(EJTAG reserved)
Reserved for future EJTAG use
0x010
TCBCONTROLA
Selects the control register TCBTraceControl in the Trace
Control Block
0x011
TCBCONTROLB
Selects another trace control block register
0x012
TCBADDRESS
Selects the address register used in the trace control
block
0x013 — 0x1B
(EJTAG reserved)
Reserved for future EJTAG use
0x01C — All 1’s
(Free for other use)
Free for other use, such as JTAG boundary scan
All 1’s
BYPASS
Select Bypass register
Table 20.41 EJTAG TAP Instruction Overview