Hello @HPC,
since Modbus doesn't know anything about data types, it is up to both the master and slave to come up with an exchange format. The registers are 16bit, but the ASCII is only 8bit. The data has to be aligned somehow, or maybe two consecutive characters can be stored into one register?
Either way, the goal will be to iterate through the string and convert every item of the string array to byte.
Best regards,
Martin