SH7751 Datasheet, PDF (918/1224 Pages) Renesas Technology Corp – 32-Bit RISC Microcomputer

20. User Break Controller (UBC)
20.6 User Break Controller Stop Function
This function stops the clock supplied to the user break controller and is used to minimize power
dissipation when the chip is operating. Note that, if you use this function, you cannot use the user
break controller.
20.6.1 Transition to User Break Controller Stopped State
Setting the MSTP5 bit of the STBCR2 (inside the CPG) to 1 stops the clock supply and causes the
user break controller to enter the stopped state. Follow steps (1) to (5) below to set the MSTP5 bit
to 1 and enter the stopped state.
(1) Initialize BBRA and BBRB to 0;
(2) Initialize BRCR to 0;
(3) Make a dummy read of BRCR;
(4) Read STBCR2, then set the MSTP5 bit in the read data to 1 and write back.
(5) Make two dummy reads of STBCR2.
Make sure that, if an exception or interrupt occurs while performing steps (1) to (5), you do not
change the values of these registers in the exception handling routine.
Do not read or write the following registers while the user break controller clock is stopped:
BARA, BAMRA, BBRA, BARB, BAMRB, BBRB, BDRB, BDMRB, and BRCR. If these
registers are read or written, the value cannot be guaranteed.
20.6.2 Cancelling the User Break Controller Stopped State
The clock supply can be restarted by setting the MSTP5 bit of STBCR2 (inside the CPG) to 0. The
user break controller can then be operated again. Follow steps (6) and (7) below to clear the
MSTP5 bit to 0 to cancel the stopped state.
(6) Read STBCR2, then clear the MSTP5 bit in the read data to 0 and write the modified data
back;
(7) Make two dummy reads of STBGR2.
As with the transition to the stopped state, if an exception or interrupt occurs while processing
steps (6) and (7), make sure that the values in these registers are not changed in the exception
handling routine.
Rev.4.00 Oct. 10, 2008 Page 820 of 1122
REJ09B0370-0400