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CHAPTER 6 JTAG BOUNDARY SCAN
User’s Manual S14054EJ4V0UM
113
6.2
Internal Configuration of Boundary Scan Circuit
Figure 6-1 shows the block diagram of the internal JTAG boundary scan circuit of the
µ
PD98431.
Figure 6-1. Block Diagram of Boundary Scan Circuit
TDO
TDI
TMS
TCK
TRST#
Boundary scan register
Bypass register
Instruction decoder
Instruction register
TAP
controller
MUX
Output buffer
6.2.1
Instruction register
The instruction register consists of a 2-bit shift register and writes instruction data from the TDI pin. The register
and instruction are selected by this instruction data.
6.2.2
TAP (Test Access Port) controller
The TAP controller changes operating state by latching the signal of the TMS pin at the rising edge of the clock
input to the TCK pin.
6.2.3
Bypass register
The bypass register consists of a 1-bit shift register connected between the TDI and TDO pins when the TAP
controller is in Shift-DR state. If this register is selected while the TAP controller is in Shift-DR state, data is shifted to
the TDO pin at the rising edge of the clock input to the TCK pin.
When this register is selected, the operation of the JTAG boundary circuit does not influence on the operation of
the
µ
PD98431.
6.2.4
Boundary scan register
The boundary scan register is located between an external pin of the
µ
PD98431 and internal logic circuit. When
this register is selected, data is latched or loaded by the instruction of the TAP controller.
If this register is selected while the TAP controller is in Shift-DR state, data is output to the TDO pin starting from
the LSB at the falling edge of the clock input to the TCK pin.
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