How to put Juno into Sleep-state

I'm using Linaro Release 15.12 LSK (without OP-TEE) + OpenEmbedded Minimal Filesystem on Juno-r1 Board.

I'm trying to put the Juno board into the Sleep-state referring to ARM Versatile Express Juno r1 Development Platform Technical Reference Manual.

But it seems to reboot and fall into the error state, even if I push the Soft Reset button briefly.

Does anyone know how to put the Juno board into the Sleep-state ?

Thank you for your help.