Motor de Búsqueda de Datasheet de Componentes Electrónicos |
|
MC908QC8CDZER Datasheet(PDF) 100 Page - Freescale Semiconductor, Inc |
|
MC908QC8CDZER Datasheet(HTML) 100 Page - Freescale Semiconductor, Inc |
100 / 274 page Oscillator Mode (OSC) MC68HC908QC16 • MC68HC908QC8 • MC68HC908QC4 Data Sheet, Rev. 2 100 Freescale Semiconductor from $FFC0 into OSCTRIM if needed. The factory trim value provides the accuracy required for communication using force monitor mode. Trimming the device in the user application board will provide the most accurate trim value. See Oscillator Characteristics in the Electrical Chapter of this data book for additional information on factory trim. 10.3.2.2 Internal to External Clock Switching When external clock source (external OSC, RC, or XTAL) is desired, the user must perform the following steps: 1. For external crystal circuits only, configure OSCOPT[1:0] to external crystal. To help precharge an external crystal oscillator, momentarily configure OSC2 as an output and drive it high for several cycles. This can help the crystal circuit start more robustly. 2. Configure OSCOPT[1:0] and ECFS[1:0] according to 10.8.1 Oscillator Status and Control Register. The oscillator module control logic will then enable OSC1 as an external clock input and, if the external crystal option is selected, OSC2 will also be enabled as the clock output. If RC oscillator option is selected, enabling the OSC2 output may change the bus frequency. 3. Create a software delay to provide the stabilization time required for the selected clock source (crystal, resonator, RC). A good rule of thumb for crystal oscillators is to wait 4096 cycles of the crystal frequency; i.e., for a 4-MHz crystal, wait approximately 1 ms. 4. After the stabilization delay has elapsed, set ECGON. After ECGON set is detected, the OSC module checks for oscillator activity by waiting two external clock rising edges. The OSC module then switches to the external clock. Logic provides a coherent transition. The OSC module first sets ECGST and then stops the internal oscillator. 10.3.2.3 External to Internal Clock Switching After following the procedures to switch to an external clock source, it is possible to go back to the internal source. By clearing the OSCOPT[1:0] bits and clearing the ECGON bit, the external circuit will be disengaged. The bus clock will be derived from the selected internal clock source based on the ICFS[1:0] bits. 10.3.3 External Oscillator The external oscillator option is designed for use when a clock signal is available in the application to provide a clock source to the MCU. The OSC1 pin is enabled as an input by the oscillator module. The clock signal is used directly to create BUSCLKX4 and also divided by two to create BUSCLKX2. In this configuration, the OSC2 pin cannot output BUSCLKX4. The OSC2EN bit will be forced clear to enable alternative functions on the pin. 10.3.4 XTAL Oscillator The XTAL oscillator circuit is designed for use with an external crystal or ceramic resonator to provide an accurate clock source. In this configuration, the OSC2 pin is dedicated to the external crystal circuit. The OSC2EN bit has no effect when this clock mode is selected. In its typical configuration, the XTAL oscillator is connected in a Pierce oscillator configuration, as shown in Figure 10-2. This figure shows only the logical representation of the internal components and may not represent actual circuitry. |
Número de pieza similar - MC908QC8CDZER |
|
Descripción similar - MC908QC8CDZER |
|
|
Enlace URL |
Política de Privacidad |
ALLDATASHEET.ES |
¿ALLDATASHEET es útil para Ud.? [ DONATE ] |
Todo acerca de Alldatasheet | Publicidad | Contáctenos | Política de Privacidad | Intercambio de Enlaces | Lista de Fabricantes All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |