Datasheet

212
ATmega32A [DATASHEET]
Atmel-8155D-AVR-ATmega32A-Datasheet_02/2014
Figure 24-2. TAP Controller State Diagram
24.4 TAP Controller
The TAP controller is a 16-state finite state machine that controls the operation of the Boundary-scan circuitry,
JTAG programming circuitry, or On-chip Debug system. The state transitions depicted in Figure 23-2 depend on
the signal present on TMS (shown adjacent to each state transition) at the time of the rising edge at TCK. The ini-
tial state after a Power-On Reset is Test-Logic-Reset.
As a definition in this document, the LSB is shifted in and out first for all Shift Registers.
Assuming Run-Test/Idle is the present state, a typical scenario for using the JTAG interface is:
• At the TMS input, apply the sequence 1, 1, 0, 0 at the rising edges of TCK to enter the Shift Instruction Register
– Shift-IR state. While in this state, shift the four bits of the JTAG instructions into the JTAG Instruction Register
from the TDI input at the rising edge of TCK. The TMS input must be held low during input of the 3 LSBs in
order to remain in the Shift-IR state. The MSB of the instruction is shifted in when this state is left by setting
TMS high. While the instruction is shifted in from the TDI pin, the captured IR-state 0x01 is shifted out on the
Test-Logic-Reset
Run-Test/Idle
Shift-DR
Exit1-DR
Pause-DR
Exit2-DR
Update-DR
Select-IR Scan
Capture-IR
Shift-IR
Exit1-IR
Pause-IR
Exit2-IR
Update-IR
Select-DR Scan
Capture-DR
0
1
0
11 1
00
00
11
1
0
1
1
0
1
0
0
1
0
1
1
0
1
0
0
00
11