S7300与S720通过EM277组态PROFIBUS通信，按照教程上说的硬件组态做好了，但是下载到S7300时提示出错：
1.The block/op. sys. update is too large.
Help Text是
Help on Message 33:279
Des cription:

ONLINE: Block cannot be stored in the load memory or the work memory of the CPU.
Note the restrictions of the CPU being used.

EPROM: Block or BESY-Update (operating system update) is too large for the remaining memory capacity on the Memory Card/MMC.

To correct or avoid errors:

Use a Memory Card/MMC with higher storage capacity for this application, provided the technical data of the CPU allows this.

2.Cannot load SDB 4.

3.The system data cannot be loaded to module
CPU 315-2 DP - (R0/S2) of station SIMATIC
300 Station.
Look under details or try to determine the
cause for the problem using the diagnostic
buffer of the module.
Help Text是：
Des cription:

No or only part of the system data was transferred to the module.
Possible Causes:

?The station configuration does not have the module that requires the SDB mentioned.

?The module is present, but it may have an incorrect firmware version (e.g. for WinLC).

Remedy:

1. Determine the cause of the error using the module抯 diagnostic buffer, and correct the error.

2. Recompile the system data.

3. Repeat the download.

网上有人说这种组态下，S7300要加MCC卡，是真的吗？
MCC好贵啊～