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如果使用內部RC振蕩器而不使用外部晶振，請按照下面方法處理： 1）對于100腳或144腳的產品，OSC_IN應接地，OSC_OUT應懸空。 2）對于少于100腳的產品，有2種接法： 2.1）OSC_IN和OSC_OUT分別通過10K電阻接地。此方法可提高EMC性能。 2.2）分別重映射OSC_IN和OSC_OUT至PD0和PD1，再配置PD0和PD1為推挽輸出并輸出'0'。此方法可以減小功耗并(相對上面2.1)節省2個外部電阻。 以下是在ST英文網站FAQ上抄下的詳細解釋： 1) In 100 and 144 packages, the OSC_IN /OSC_Out pins are a dedicated pins for HSE and mapped respectively on pins 12, 13 and pins 23, 24 for LQFP packages. Although, for BGA 100 and BGA 144 packages, they are mapped respectively on pins C1,D1 and pins D1,E1. In this case the recommended configuration is: OSC_In pin must be connected to ground as it is always an input pin OSC_Out must be left not connected as it is always an output pin. 2) In LQFP48 and LQFP64 packages, the OSC_IN/OSC_Out pins are mapped on pins 5,6 whereas in the VFQFPN36 package they are mapped on pins 2,3. However the PD0 and PD1 functionality can be remapped by software on these pins. There are two possible configurations: Hardware configuration: Connect the OSC_IN/OSC_Out pins to ground through a 10K pull down resistors. Software configuration: First, the OSC_IN/OSC_Out pins are left not connected on PCB layout. Then, remap the PD0 and PD1 functionality by software on these pins and configure the PD0/PD1 to Output push-pull forced to 0 logic level(Data Register = 0). This will maintain those I/Os to a fixed level minimizing Noise and external stress on these pins. The software configuration is recommended to reduce the power consumption and saves cost by avoiding the use of external pull down resistors as the I/O is already connected to the ground internally. Whereas the hardware configuration is recommended to increase the EMC performance. 發表于 2009/3/28 |
