Datasheet

Section 15 Serial Communication Interface (SCI, IrDA)
Rev. 3.00 Mar 17, 2006 page 728 of 926
REJ09B0283-0300
Specified pulse width
SCK
CKE0
Specified pulse width
Figure 15.31 Timing for Fixing Clock Output Level
When turning on the power or switching between Smart Card interface mode and software standby
mode, the following procedures should be followed in order to maintain the clock duty cycle.
Powering On: To secure the clock duty cycle from power-on, the following switching procedure
should be followed.
1. The initial state is port input and high impedance. Use a pull-up resistor or pull-down
resistor to fix the potential.
2. Fix the SCK pin to the specified output level with the CKE1 bit in SCR.
3. Set SMR and SCMR, and switch to smart card mode operation.
4. Set the CKE0 bit in SCR to 1 to start clock output.
When changing from smart card interface mode to software standby mode:
1. Set the data register (DR) and data direction register (DDR) corresponding to the SCK pin
to the value for the fixed output state in software standby mode.
2. Write 0 to the TE bit and RE bit in the serial control register (SCR) to halt transmit/receive
operation. At the same time, set the CKE1 bit to the value for the fixed output state in
software standby mode.
3. Write 0 to the CKE0 bit in SCR to halt the clock.
4. Wait for one serial clock period.
During this interval, clock output is fixed at the specified level, with the duty cycle
preserved.
5. Make the transition to the software standby state.