M37733MHBXXXFP Datasheet, PDF (54/89 Pages) Mitsubishi Electric Semiconductor – SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

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MITSUBISHI MICROCOMPUTERS
M37733MHBXXXFP
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
OSCILLATION CIRCUIT
In the oscillation circuit, two kinds of clock circuits are built-in. One is
the main-clock oscillation circuit which uses the XIN and XOUT pins,
and the other is the sub-clock (32 kHz) oscillation circuit which uses
the XCIN and the XCOUT pins.
Either of these two oscillation circuits can output the system clock,
and it can be selected.
Figure 61 shows the oscillation circuit example with a ceramic
resonator or a quartz-crystal oscillator connected. The circuit
constants such as capacitance depend on a resonator/oscillator, and
these constants shall be set to the resonator/oscillator manufacture’s
recommended value.
Figure 62 shows the example of the external clock input circuit.
When inputting the main clock externally, the main-clock oscillation
circuit stops operating and power dissipation could be conserved by
setting the main clock external input selection bit (bit 1 of the oscillation
circuit control register 1, refer to Figure 63) to “1”. Note that this bit
also has the function to select a return factor from STP state (refer to
the section on the STANDBY FUNCTION.) Additionally, write to the
oscillation circuit control register 1 as the flow shown in Figure 64.
Pins XCIN and XCOUT of the sub-clock oscillation circuit are also used
as I/O ports P77 and P76, and these functions are selected with the
port-XC selection bit described below.
From the time during reset to the time after releasing reset, only the
main-clock oscillation circuit operates and the main clock is selected
as the system clock. Furthermore, at this time, the sub-clock oscillation
circuit stops and pins XCIN and XCOUT become I/O ports (P77, P76).
When the port-XC selection bit (bit 4 of the oscillation circuit control
register 0) is set to “1” in this condition, I/O ports P77 and P76 are
switched to pins XCIN and XCOUT, and then, oscillation starts in the
sub-clock oscillation circuit.
XIN
XOUT
Left open
XCIN
P76
(P76 as I/O port)
External oscillation circuit External oscillation circuit
Vcc
Vcc
Vss
Vss
• When inputting the main clock externally, set the main clock
external input selection bit to “1”. Then, leave the XOUT pin
open.
• When inputting the sub clock externally, set the sub-clock
external input selection bit to “1”. Then, port P76 becomes an
I/O port.
Fig. 62 External clock input circuit
When inputting the sub clock externally, set the sub-clock external
input selection bit (bit 2 of the oscillation circuit control register 1) to
“1” before selecting pins XCIN and XCOUT with the port-Xc selection
bit. When the sub-clock external input selection bit is set to “1”, port
P76 becomes an I/O port (or an analog input AN6). Note that this bit
also has the function to select a return factor from STP state (refer to
the section on the STANDBY FUNCTION.)
When the sub-clock output selection bit (bit 1 of the port function
control register, refer to Figure 11) is set to “1” under the condition of
the port-Xc selection bit = “1”, the sub-clock φ SUB is output from port
P67. Accordingly, the sub-clock 32 kHz can be supplied for external
devices.
XIN
XOUT
Rf
XCIN
XCOUT
Rcf
Rd
Rcd
(32 kHz)
CIN
COUT
CCIN
CCOUT
In this case, sub-clock oscillation circuit is used.
(Port-Xc selection bit is “1”)
XIN
XOUT
Rf
Rd
P77
P76
(P77, P76 as I/O port)
CIN
COUT
In this case, sub-clock oscillation circuit is not used.
( Port-Xc selection bit is “0”)
Fig. 61 Oscillation circuit example with external resonator or quartz-crystal oscillator
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