IDT EJTAG System
EJTAG Test Access Port
79RC32438 User Reference Manual
20 - 57
November 4, 2002
Notes
Test-Logic-Reset State
When the Test-Logic-Reset state is entered, the Instruction register is loaded with the IDCODE instruc-
tion, and any EJTAGBOOT indication is cleared. This state ensures that the TAP does not interfere with the
normal operation of the CPU core. The TAP controller always reaches this state after five rising edges on
JTAG_TCK when JTAG_TMS is set to 1. A low value on JTAG_TRST_N immediately places the TAP
controller in this state asynchronous to JTAG_TCK.
Capture-IR State
In the Capture-IR state, the two LSBs of the Instruction register are loaded with the value 012, and the
upper MSBs are loaded with implementation-dependent values. Both values are loaded on the rising edge
of JTAG_TCK.
Shift-IR State
In the Shift-IR state, the LSB of the Instruction register is output on JTAG_TDO on the falling edge of
JTAG_TCK. The Instruction register is shifted one position from MSB to LSB on the rising edge of
JTAG_TCK, with the MSB shifted in from JTAG_TDI. The value in the Instruction register does not take
effect until the Update-IR state. Figure 20.24 shows the shifting direction for the Instruction register.
Figure 20.24 JTAG_TDI to JTAG_TDO Path in Shift Mode State
The length of the Instruction register is specified in section “Instruction Register and Special Instruc-
tions” on page 20-58. The value loaded in the Capture-IR state is used as the initial value for the Instruction
register when shifting starts. Thus, it is not possible to read out the previous value of the Instruction register.
Update-IR State
In the Update-IR state, the value in the Instruction register takes effect on the rising or falling edge of
JTAG_TCK.
Capture-DR State
In the Capture-DR state, the value of the selected data register(s) is captured on the rising edge of
JTAG_TCK for shifting out in the Shift-DR state. The Capture-DR state reads the data, in order to output
this read value in the Shift-DR state. The Instruction register controls the selection of the following data
register(s): Bypass, Device ID, Implementation, EJTAG Control, Address, and Data register(s).
Shift-DR State
In the Shift-DR state, the LSB of the selected data register(s) is output on JTAG_TDO on the falling edge
of JTAG_TCK. The selected data register(s) is shifted one position from MSB to LSB on the rising edge of
JTAG_TCK, with JTAG_TDI shifted in at the MSB. The value(s) shifted into the register(s) does not take
effect until the Update-DR state. Figure 20.25 shows the shifting direction for the selected data register.
Figure 20.25 JTAG_TDI to JTAG_TDO Path for Selected Data Register(s) in Shift-DR State
The length of the shift path depends on the selected data register(s).
Update-DR State
In the Update-DR state, the update of the selected data register(s) with the value from the Shift-DR state
occurs on the falling or rising edge of JTAG_TCK. This update writes the selected register(s).
JTAG_TDI
Instruction Register
MSB
0 / LSB
JTAG_TDO
MSB
0 / LSB
JTAG_TDI
JTAG_TDO
Selected Data Register(s)