This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

sys_clkreq pin ... a input or output ?

Other Parts Discussed in Thread: AM3517

Hi

Say we are using an external CMOS digital clock through the sys_xtalin pin. In this case, the sys_clkreq is used as an output to request the external system clock.

(1) Page 70 of datasheet – A CMOS digital clock through the sys_xtalin pin. In this case, the sys_clkreq is used as an output to request the external system clock.

Now, I want the same 26MHz clock seen on the sys_clkout1, such that it can be used by a downstream device. As per the Datasheet, we can do so by either SW register control( I donot want to use SW control) or by asserting the sys_clkreq. The downstream device, always needs to see this clock , regardless of the CPU being in Active state or Power down state.

(2) Page 73, In section "4.3 Output Clock Specifications" of the DataSheet, it says -

sys_clkout1 can output the oscillator clock (26 MHz) at any time. It can be controlled by software or externally using sys_clkreq control. When the device is in the off state, the sys_clkreq can be asserted to enable the oscillator and activate the sys_clkout1 without waking up the device. The off state polarity of sys_clkout1 is programmable.

The use of this sys_clkreq as a output for clock request in statement (1)  seems confusing to it's use as an input in statement (2).

Am I missing something here? Could someone please explain this.

Thanks,

Pretesh

  • I believe the explanation you are looking for is in section 4.7.5.1 of SPRUGR0, the AM3517 TRM. Essentially the pin is bi directional, and will be an input or an output depending on various conditions, table 4-27 in that section provides the various conditions that sys_clkreq will be either an input or an output.