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M37151M6 Datasheet(PDF) 93 Page - Renesas Technology Corp |
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M37151M6 Datasheet(HTML) 93 Page - Renesas Technology Corp |
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93 / 138 page  M37151M6/M8/MA/MC/MF-XXXFP, M37151EFFP Rev.1.00 Nov 01, 2002 page 93 of 136 REJ03B0129-0100Z 8.14 CLOCK GENERATING CIRCUIT This microcomputer has 2 built-in oscillation circuits. An oscillation circuit can be formed by connecting a resonator between XIN and XOUT (XCIN and XCOUT). Use the circuit constants in accordance with the resonator manufacturer’s recommended values. No external re- sistor is needed between XIN and XOUT since a feed-back resistor exists on-chip. However, an external feed-back resistor is needed between XCIN and XCOUT. When using XCIN-XCOUT as sub-clock, clear bits 5 and 6 of the OSD control register to “0.” To supply a clock signal externally, input it to the XIN (XCIN) pin and make the XOUT (XCOUT) pin open. When not using XCIN clock, connect the XCIN to VSS and make the XCOUT pin open. The OSD clock can be chosen to be the data slicer clock (approx. 26 MHz) that is output from the data slicer. After reset has completed, the internal clock φ is half the frequency of XIN. Immediately after poweron, both the XIN and XCIN clock start oscillating. To set the internal clock φ to low-speed operation mode, set bit 7 of the CPU mode register to “1.” 8.14.1 OSCILLATION CONTROL (1) Stop Mode The built-in clock generating circuit is shown in Figure 120. When the STP instruction is executed, the internal clock f stops at HIGH. At the same time, timers 3 and 4 are connected by hardware and “FF16” is set in timer 3 and “0716” is set in timer 4. Select f(XIN)/16 or f(XCIN)/ 16 as the timer 3 count source (set both bit 0 of timer mode register 2 and bit 6 at address 00C716 to “0” before the execution of the STP instruction). Moreover, set the timer 3 and timer 4 interrupt enable bits to disabled (“0”) before execution of the STP instruction. The oscillator restarts when an external interrupt is accepted. However, the internal clock f keeps its HIGH level until timer 4 overflows, allow- ing time for oscillation stabilization when a ceramic resonator or a quartz-crystal oscillator is used. By settimg bit 7 of timer return setting register (address 00CC16) to “1, ” an arbitrarary value can be set to timer 3 and timer 4. Bit 7 of clock control register 3 (address 020216) can switch Port P10 pin and the CLKCONT. When CLKCONT pin is selected, “H” is output normally. When an extenal interrupt is recieved in the STP state, the CLKCONT pin goes back to “H” output. (2) Wait Mode When the WIT instruction is executed, the internal clock φ stops in the HIGH level but the oscillator continues running. This wait state is released at reset or when an interrupt is accepted (See note). Since the oscillator does not stop, the next instruction can be executed immediately. Note: In the wait mode, the following interrupts are invalid. • VSYNC interrupt • OSD interrupt • All timer interrupts using external clock input from port pin as count source • All timer interrupts using f(XIN)/2 or f(XCIN)/2 as count source • All timer interrupts using f(XIN)/4096 or f(XCIN)/4096 as count source • f(XIN)/4096 interrupt • Multi-master I2C-BUS interface interrupt • Data slicer interrupt • A-D conversion interrupt (3) Low-speed Mode If the internal clock is generated from the sub-clock (XCIN), a low power consumption operation can be realized by stopping only the main clock XIN. To stop the main clock, set bit 6 (CM6) of the CPU mode register (00FB16) to “1.” When the main clock XIN is restarted, the program must allow enough time for oscillation to stabilize. Note that in the low-power-consumption mode the XCIN-XCOUT drivability can be reduced, allowing even lower power consumption. To reduce the XCIN-XCOUT drivability, clear bit 5 (CM5) of the CPU mode register (00FB16) to “0.” At reset, this bit is set to “1” and strong drivability is selected to help the oscillation to start. When executing an STP instruction, set this bit to “1” by software before initiating the instruction. Fig.8.14.1 Ceramic Resonator Circuit Example Fig.8.14.2 External Clock Input Circuit Example XCIN XIN CCIN Microcomputer XCOUT Rf Rd CCOUT XOUT CIN COUT C1 0.01µF FILT XCIN Microcomputer External oscillation circuit or external pulse XCOUT XIN XOUT Open Open External oscillation circuit Vcc Vss Vcc Vss |
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