FS05以下可以随意升降，FS05及其以上不可以降

 https://support.industry.siemens.com/cs/cn/en/view/107247170

 Update V4.2.0

Key features supported by S7-1200 CPU firmware V4.2.0 include:

Enhancements to the Web server

New programming instructions including 2 new basic instructions and 24 extended instructions

New communication capabilities

Backup and restore of an online S7-1200 CPU and F-CPU from STEP 7

New high-speed counter (HSC) capabilities

Enhancements to capturing and loading an online DB snapshot

Reduction of repeated security event entries in the diagnostics buffer

Required software: TIA Portal with STEP 7 V14 Basic or STEP 7 V14 Professional

NOTICE: S7-1200 CPUs with Functional Stand 05 (FS: 05) or later cannot be downgraded to firmware versions prior to V4.2.0.