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ST92F124 数据表(PDF) 138 Page - STMicroelectronics |
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ST92F124 数据表(HTML) 138 Page - STMicroelectronics |
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138 / 429 page  138/429 ST92F124/F150/F250 - RESET AND CLOCK CONTROL UNIT (RCCU) 7.5 CRYSTAL OSCILLATOR The on-chip components for the crystal oscillator are an inverting circuit, polarised at the trip point. The inverter is built around an n-channel transis- tor, loaded with a current source and polarised through a feedback resistor. The current source is tailored to obtain a pseudo sinusoidal signal at OSCOUT and OSCIN, reduc- ing the electromagnetic emission. The inverter stage is followed by a matching inverter, which is followed in turn by a schmitt-triggered buffer. In HALT mode, set by means of the HALT instruc- tion, in STOP mode, and under control of the XT- STOP bit, the oscillator is disabled. The current sources are switched off, reducing the power dis- sipation. The internal clock, CLOCK1, is forced to a high level. To exit the HALT condition and restart the oscilla- tor, an external RESET pulse is required, having a a minimum duration of TSTUP (see Figure 70 and Section 11 ELECTRICAL CHARACTERISTICS). It should be noted that, if the Watchdog function is enabled, a HALT instruction will not disable the os- cillator. This to avoid stopping the Watchdog if a HALT code is executed in error. When this occurs, the CPU will be reset when the Watchdog times out or when an external reset is applied. Figure 66. Crystal Oscillator Table 31. Maximum RS values Legend: C1, C2: Maximum Total Capacitances on pins OSCIN and OSCOUT (the value includes the external capacitance tied to the pin plus the parasitic capacitance of the board and of the device) Note: The tables are relative to the fundamental quartz crystal only (not ceramic resonator). Figure 67. Internal Oscillator Schematic Figure 68. External Clock OSCIN OSCOUT C1 C2 ST9 CRYSTAL CLOCK *Rd can be inserted to reduce the drive level, Rd* when using low drive crystals. hi l d i t l C1=C2 Freq. 33pF 22pF 5 MHz 80 130 4 MHz 120 200 3 MHz 220 370 OSCOUT RPOL VDD ILOAD OSCIN CLOCK1 OSCOUT OSCIN CLOCK INPUT EXTERNAL CLOCK VR02116B ST9 9 |
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