M306H7MG-XXXFP Datasheet, PDF (27/329 Pages) Renesas Technology Corp – SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER with DATA ACQUISITION CONTROLLER

M306H7MG-XXXFP/MC-XXXFP/FGFP
4. CLOCK GENERATION CIRCUIT
System clock control register 0 (Note 1)
b7 b6 b5 b4 b3 b2 b1 b0
Symbol
CM0
Address
000616
After reset ^{(Note 14)}
011110002 (STARTB pin = Vcc)
010010002 (STARTB pin = Vss)
Bit symbol
Bit name
CM00
CM01
Clock output function
select bit
(Valid only in single-chip
mode)
CM02
WAIT peripheral function
clock stop bit (Note 10)
Function
RW
b1 b0
0 0 : I/O port P57
RW
0 1 : fC output
1 0 : f8 output
1 1 : f32 output
RW
0 : Do not stop peripheral function clock in wait mode
1 : Stop peripheral function clock in wait mode (Note 8)
RW
CM03
XCIN-XCOUT drive capacity 0 : LOW
select bit (Note 2)
1 : HIGH
RW
CM04
Port XC select bit
(Note 2)
0 : I/O port P86, P87
1 : XCIN-XCOUT generation function(Note 9)
RW
CM05
Main clock stop bit
(Notes 3, 10, 12, 13)
0 : On
1 : Off (Note 4, Note5)
RW
CM06
Main clock division select 0 : CM16 and CM17 valid
bit 0 (Notes 7, 13)
1 : Division by 8 mode
RW
CM07
System clock select bit
(Notes 6, 10, 11, 12)
0 : Main clock
1 : Sub-clock
RW
Note 1: Write to this register after setting the PRC0 bit of PRCR register to “1” (write enable).
Note 2: The CM03 bit is set to “1” (high) when the CM04 bit is set to “0” (I/O port) or the microcomputer goes to a stop mode.
Note 3: This bit is provided to stop the main clock when the low power dissipation mode is selected. This bit cannot be used for
detection as to whether the main clock stopped or not. To stop the main clock, the following setting is required:
(1) Set the CM07 bit to “1” (Sub-clock select) with the sub-clock stably oscillating.
(2) Set the CM05 bit to “1” (Stop).
Note 4: During external clock input, only the clock oscillation buffer is turned off and clock input is accepted if the sub clock is not
chosen as a CPU clock.
Note 5: When CM05 bit is set to “1, the XOUT pin goes “H”. Furthermore, because the internal feedback resistor remains connected,
the XIN pin is pulled “H” to the same level as XOUT via the feedback resistor.
Note 6: After setting the CM04 bit to “1” (XCIN-XCOUT oscillator function), wait until the sub-clock oscillates stably before switching
the CM07 bit from “0” to “1” (sub-clock).
Note 7: When entering stop mode from high or middle speed mode, the CM06 bit is set to “1” (divide-by-8 mode).
Note 8: The fC32 clock does not stop. During low speed or low power dissipation mode, do not set this bit to “1” (peripheral clock
turned off when in wait mode).
Note 9: To use a sub-clock, set this bit to “1”. Also make sure ports P8 6 and P87 are directed for input, with no pull-ups.
Note 10: When the PM21 bit of PM2 register is set to “1” (clock modification disable), writing to the CM02, CM05, and CM07 bits has
no effect.
Note 11: If the PM21 bit needs to be set to “1”, set the CM07 bit to “0”(main clock) before setting it.
Note 12: To use the main clock as the clock source for the CPU clock, follow the procedure below.
(1) Set the CM05 bit to “0” (oscillate).
(2) Wait until td(M-L) elapses or the main clock oscillation stabilizes, whichever is longer.
(3) Set the CM07 bit all to “0”.
Note 13: When the CM05 bit is set to “1” (main clock turned off), the CM06 bit is fixed to “1” (divide-by-8 mode) and the
CM15 bit is fixed to “1” (drive capability high).
Note 14: Keep in mind that the values after reset differ by the input voltage at the STARTB pin.
Figure 4.2 CM0 Register
Rev.2.10 Oct 25, 2006 Page 27 of 326
REJ03B0152-0210