Clock Output Control; Figure 14.31 Timing For Fixing Clock Output Level - Renesas H8S Series Hardware Manual

Section 14 Serial Communication Interface (SCI)
14.7.8

Clock Output Control

When the GM bit in SMR is set to 1, the clock output level can be fixed with bits CKE0 and
CKE1 in SCR. At this time, the minimum clock pulse width can be made the specified width.
Figure 14.31 shows the timing for fixing the clock output level. In this example, GM is set to 1,
CKE1 is cleared to 0, and the CKE0 bit is controlled.
CKE0
SCK
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.
Powering On: To secure clock duty 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 preserved.
5. Make the transition to the software standby state.
Rev. 6.00 Mar 15, 2006 page 374 of 570
REJ09B0211-0600
Specified pulse width

Figure 14.31 Timing for Fixing Clock Output Level

Specified pulse width