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IDT EJTAG System
EJTAG Test Access Port
79RC32438 User Reference Manual
20 - 71
November 4, 2002
Notes
Figure 20.34 TAP Operation Example
The five-bit Instruction register is initially loaded with 000012. The first bit shifted out of the Instruction
register is a 1 followed by four 0’s. IR0 to IR4 indicate the new value for the Instruction register. IR0, the
new LSB, is shifted in first, because it will be at the LSB position once all five bits are shifted in. This
example is similar for the selected data register.
ManufID Value
Table 20.51shows the values of the ManufID field in the Device ID register as defined by the manufac-
turer. The Device ID register is described in
section “Device Identification (ID) Register (TAP Instruction
IDCODE)” on page 20-61.
Rocc Bit Usage
The R/W0 Rocc bit in the EJTAG Control register acknowledges that the probe has seen a processor
reset, and further accesses take this reset into account. This bit is set at reset. The probe must clear it as an
acknowledge of the reset. All other writes to the EJTAG Control register, except for the reset acknowledge,
should write 1 to this bit in order to not acknowledge any resets occurring between reads and writes of the
EJTAG Control register. Correct use of the Rocc bit ensures safe handling of processor access even across
reset. An example is the following scenario:
1. A processor access is pending and the PrAcc is read with value 1 (Rocc has been cleared previ-
ously).
2. The Address and Data registers are accessed and set up to handle the processor access.
3. The EJTAG Control register is accessed to finish the processor access. The register is read in the
Capture-DR state. Shifting in of the value to write begins.
Company
JDEC Code
Continuations
Last Byte
Without Carry
ManufID
Value
IDT
0xB3
0
0x33
0x33
Table 20.51 ManufID Field Value Example
R
JTAG_TCK
S
C
S
E
U
S
C
S
S
JTAG_TMS
JTAG_TDI
JTAG_TDO
TAP
controller
IR0
IR1
IR2
IR3
IR4
DR0
DR1
DR2