19.2.9.4.1 Read ROM Code Version
For this specific command, the Secure SAM-BA Monitor replies with the SVER opcode, and indicates that the ROM code version string length is 30 bytes, so the external tool knows how many character should be received.
(PC to device) >> RVER,0,0,0,00#
(Device to PC) << SVER,00000000,00000030#v1.0............Jul
26 2019.....011:14:22........