Datasheet

Section 13 Boundary Scan Function
Rev.7.00 Dec. 24, 2008 Page 463 of 698
REJ09B0074-0700
13.5 Usage Notes
1. When using the boundary scan function, clear TRST to 0 at power-on and after the t
RESW
time
has elapsed set TRST to 1 and set TCK, TMS, and TDI appropriately. During normal operation
when the boundary scan function is not used, set TCK, TMS, and TDI to Hi-Z, clear TRST to 0
at power-on, and after the t
RESW
time has elapsed set TRST to 1 or to Hi-Z. These pins are
pulled up internally, so care must be taken in standby mode because breakthrough current flow
can occur if there is a potential difference between the pin input voltage value when set to 1
and the power supply voltage Vcc.
2. The following must be noted on the power-on reset signal applied to the TRST pin.
• Reset signal must be applied at power-on.
• TRST must be separated in order not to affect the system operation.
• TRST must be separated from the system circuitry in order not to affect the system
operation.
• System circuitry must also be separated from the TRST in order not to affect TRST
operation as shown in figure 13.4.
Board edge pin
System
reset
TRST
TRST
RES
LSI
Power-on
reset circuit
Figure 13.4 Recommended Reset Signal Design
3. TCK clock speed should be slower than system clock frequency.
4. In serial communication, data is input or output from the LSB as shown in figure 13.5.
Boundary scan register
Bit n
Bit n - 1
Bit 1
Bit 0
TDI
TDO
Figure 13.5 Serial Data Input/Output