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7548 Datasheet(PDF) 43 Page - Renesas Technology Corp |
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7548 Datasheet(HTML) 43 Page - Renesas Technology Corp |
43 / 73 page Rev.2.00 Mar 15, 2007 Page 43 of 70 REJ03B0210-0200 7548 Group PRELIMINARY Notice: This is not a final specification. Some parametric limits are subject to change. Clock Circuit The clock circuit includes the XIN clock (ceramic oscillator or crystal oscillator can be used), XCIN clock (32 kHz oscillator can be used), external clock input, high-speed on-chip oscillator, and low-speed on-chip oscillator. Pins P20/XOUT/XCOUT and P21/XIN/XCIN can be shared for the ports, XIN oscillation, and XCIN oscillation. Use the oscillation method selection bits (bits 1 and bit 0 in function set ROM data 1 (FSROM1)) to set the function of these pins. • Ceramic Resonator or Crystal Oscillator Set the oscillation method selection bits (bits 1 and bit 0 in FSROM1) to “012”, and connect the resonator (or the oscillator) and external circuit with the shortest wiring length possible. The constants of the oscillator circuit differ depending on the resonator. Use the values recommended by the resonator manufacturer. (An external feedback resistor may be necessary under some conditions.) Setting the XIN/XCIN oscillation control bit to “0” starts oscillation. This bit is sets to “0” after reset. • 32 kHz Crystal Oscillator Set the oscillation method selection bits to “102”, and connect the 32 kHz crystal oscillator and external circuit with the shortest wiring length possible. The constants of the oscillator circuit differ depending on the resonator. Use the values recommended by the resonator manufacturer. (An external feedback resistor may be necessary under some conditions.) Setting the XIN/XCIN oscillation control bit to “0” starts oscillation. This bit is sets to “0” after reset. • External Clock Input Set the oscillation method selection bits to “112”, and connect the clock source to the P20/XOUT pin. In this case, the P21/XIN pin can be used as an I/O port. • High-Speed On-Chip Oscillator The high-speed on-chip oscillator is stopped after reset. Setting the high-speed on-chip oscillator oscillation control bit (bit 1 in CLKM) to “0” starts oscillation. This bit is sets to “1” after reset. • Low-Speed On-Chip Oscillator The low-speed on-chip oscillator automatically starts oscillating after reset. Setting the low-speed on-chip oscillator oscillation control bit (bit 0 in CLKM) to “1” stops oscillation. This bit is sets to “0” after reset. If the low-speed on-chip oscillator control bit (bit 4 in FSROM2) is set to “0” and stopping the low-speed on-chip oscillator is disabled, the low-speed on-chip oscillator oscillation control bit cannot be set to “1” and oscillation cannot be stopped. Also, the oscillator does not stop even when the STP instruction is executed. • Using No Oscillator Pins (P20 as output port and P21 as I/O port) To use only an internal on-chip oscillator, set the oscillation method selection bits to “002”. The P20/XOUT pin can be used as an output port and the P21/XIN pin can be used as an I/O port. Fig 58. Structure of function set ROM data 1 Fig 59. External circuit of ceramic resonator Fig 60. External circuit of 32 kHz quarts-crystal oscillator Fig 61. External clock input circuit Oscillation method selection bits (Note 1) b1 b0 0 0: Clock pins not used (P20/XOUT and P21/XIN are used as I/O ports) 0 1: Ceramic resonator or quarts-crystal oscillator 1 0: 32 kHz quarts-crystal oscillator 1 1: External clock input (P21/XIN pin is used as I/O port) Low voltage detection circuit valid bit in the stop mode (Note 2) 0: Low voltage detection circuit invalid in the stop mode 1: Low voltage detection circuit valid in the stop mode Set “0” to these bits certainly. Set “1” to this bit certainly. b7 Function set ROM data 1 FSROM1 (FFD916) b0 Notes 1: The P20/XOUT and P21/XIN pins build in an on-chip oscillator. Even if these pins are used as I/O ports, the oscillator circuit is enabled when the MCU’s Vcc voltage drops below the operation limit voltage. In this case these pins may output undefined values. 2: When the Low voltage detection circuit is set to be valid in the stop mode, the dissipation current in the stop mode is increased. M37548 XIN XOUT Rd COUT CIN Insert a damping resistor if required. The resistance will vary depending on the oscillator and the oscillation drive capacity setting. Use the value recommended by the maker of the oscillator. Also, if the oscillator manufacturer’s data sheet specifies that a feedback resistor be added external to the chip though a feedback resistor exists on- chip, insert a feedback resistor between XIN and XOUT following the instruction. M37548 XCIN XCOUT Rd COUT CIN Insert a damping resistor if required. The resistance will vary depending on the oscillator and the oscillation drive capacity setting. Use the value recommended by the maker of the oscillator. Also, if the oscillator manufacturer’s data sheet specifies that a feedback resistor be added external to the chip though a feedback resistor exists on-chip, insert a feedback resistor between XIN and XOUT following the instruction. M37548 P21 XOUT I/O port External oscillation circuit Vcc Vss Connect the external clock to the P20/XOUT pin, not the P21/XIN pin. |
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