If you upgrade the memory to M2018P, it adds 7750 x 16-bit words of non-volatile storage to the T100MD+ PLC. That's about the maximum about of non-volatile memory T100MD888+ can support.
If you use Nano-10 PLC with FRAM-RTC, there are 11K words of FRAM memory plus 4K words of DM (can be made non volatile), giving you a total of 15K words per PLC.
Since each Nano-10 has 4 digital inputs, you can use two Nano-10 per site, each to handle 3 inputs. That means about 5K words per input - you are almost there
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If you can find a flash memory drive that accept formatted data inputs from its RS232 then certainly our PLCs use the PRINT command to send data to these kind of devices. However, such devices are getting harder to find in an increasingly network world. When devices are connected to the network/internet there is rarely a need to physically attach external memory devices to PLC anymore since data can be moved about electronically. Even in remote location devices are increasingly connected to the network via cellular modem, 3G modem etc.
Note:
There are other peripheral products under development including some prototypes of large EEPROM, and flash etc. Not all are expected to be made into final products but if there are OEM interests (read: medium to large annual qty demand) we may be able to provide customized solution. You can email to support@tri-plc.com with more details about your applications and see if we can suggest something.