AM335X 使用外部时钟芯片，32.768K晶振要不要接？

lvsetianya1

Prodigy 170 points

Other Parts Discussed in Thread: TPS65910

大家好：

1、AM335X 使用外部时钟芯片PCF8563，不用内部的RTC，但是要用PMIC_POWER_EN控制TPS65910输出，32.768K晶振要不要接？不接会有什么影响？

2、如果不用外部唤醒，EXT_WAKEUP能悬空吗？

我看官网开发板，RTC-Only-Mode ,CAP_VDD_RTC接1uF电容到地，但是PDF上“OSC1 Start-up Time”显示，CAP_VDD_RTC

电压是高电平后，晶振才能起振啊，但是CAP_VDD_RTC接1uF电容到地，不能拉高了吧，那外接的32.768K的晶振有什么作用？求解惑！

8 年多前

0 Eggsy Pang 8 年多前

TI__Genius 9922 points

这里有你所有的答案：

http://processors.wiki.ti.com/index.php/AM335x_Schematic_Checklist

External Interrupt (EXTINTn)

This signal is active high for PG1.0 and active low for PG2.x. Boards designed to support all silicon revisions may want contain population options for both in case you move between different revisions of the AM335x during development. New designs are expected to use only PG2.1.
This signal connects directly to the Cortex A8 interrupt controller, which as a result makes this a level sensitive pin. It is recommended to consider using a GPIO signal instead of EXTINTn. The GPIO pins offer more flexibility with respect to polarity as well as the ability to be edge triggered.

Ethernet

While no series resistors are required for MII/RMII/RGMII, it is prudent include zero-Ohm stuff options for the TX and RX lines. Ideally, these option resistors should be as small as possible (0402 or smaller recommended) and should be placed as close to the transmitter as possible.

RTC

The following table describes what to do with each pin related to RTC functionality. Three use case scenarios are provided:

RTC-only mode: If you will be using the low power RTC-only mode. This use case allows low power operation of the AM335x by allowing only the RTC power supply to be ON while all the remaining supplies are OFF.
RTC timer functionality but no RTC-only mode: If you will be using the RTC feature but do not need RTC-only mode. This use case allows you to use the Real Time clocking features (eg, keeping time), but you do not need to support the low power RTC-only mode.
RTC feature disabled: If you will never use the RTC features. In this use case, the RTC functions are fully disabled.

Pin	Function	RTC-only mode	RTC timer functionality but no RTC-only mode	RTC feature disabled
VDDS_RTC	1.8 V power supply	Always on RTC 1.8 V power supply	any AM335x 1.8 V power supply³⁾	any AM335x 1.8 V power supply³⁾
CAP_VDD_RTC	RTC core voltage input/LDO output¹⁾	1 uF decoupling capacitor to VSS	VDD_CORE⁴⁾	VDD_CORE⁴⁾
RTC_KALDO_ENn	Internal LDO enable input	VSS	VDDS_RTC	VDDS_RTC
RTC_PWRONRSTn	RTC power on reset input	1.8 V RTC power on reset²⁾	1.8 V PWRONRSTn ⁵⁾	VSS
PMIC_POWER_EN	PMIC power enable output	PMIC power enable input	No Connect	No Connect
EXT_WAKEUP	External wakeup input	1.8 V wakeup event signal	VSS	VSS
Datasheet power up sequencing		Figure 4-1, 2, 3	Figure 4-4	Figure 4-5

Note

0 lvsetianya1 8 年多前回复 Eggsy Pang

Prodigy 170 points

非常感谢您的及时答复！这个文档我看过了，我想用PMIC_POWER_EN控制电源芯片使能输出，只能用“RTC-Only-Mode”，但是不用内部RTC时钟，我通过IIC外接了一个时钟芯片。RTC_XTALIN 和 RTC_XTALOUT 脚怎样接呢？是下图checklist文档里的那种情况？内部RTC没有，为什么还要外供一个32.768k的时钟呢？