Can map these data blocks to MODBUS REGISTERS?

Hi,

you must pay attention, which addresses your communication partner uses. If the communication partner has specified modbus addresses, you must use these addresses (not addresses defined by yourself).

E.g. when in your communication partner a value is stored in holding register 40001 (1 word) and you want to read out it, so you must define address 0 in the parameter datablock. The data block, in which the modbus value is mapped, is your own decision. You can use DB11 or another datablock number.

It is important, that the modbus addresses in S7 are absolute addresses, without the offset 40001. The modbus block in S7 can manage the whole holding register address area 0-65535. Devices, which use the offset 40001, can only manage 40001-49999 (9999 holding register).

Wüstenräuber

Hi,

no, the datablock for the modbus register must be a global datablock, not an instance datablock. You parameterize, which modbus register are stored in DB1 (this is the mapping "register = S7 data block) and then you need only the modbus register addresses. 
E.g. Holding Register 0 to 100 is stored in DB1. The communication partner sends a request to read holding register 5 and 6. The modbus block receives the request, takes the values from the datablock from the correct address in the datablock and sends the values to the communication partner. The partner doesn't need to know, in which datablock the modbus registers are stored. This is the job of the modbus block. 

FB100 is a very, very old modbus block and it is no longer sold and no longer supported. For each CPU you need a new license and it is not allowed to copy it into a new CPU without a new license. If you now try to use FB100, then it is clear, that you copied it. 

Wüstenräuber

Hi,

yes, you need the FB for modbus communication. S7-300 and S7-400 don't support the modbus protocol without FB.
The variant is dependent on your hardware: https://support.industry.siemens.com/cs/ww/en/view/104946406

Wüstenräuber