Interfacing to the Raspberry Pi via ASCII strings

Carberry Board, communicates with Raspberry Pi microcomputer, with a full duplex serial line (UART). Carberry side of the UART, acts like a server, that receive commands from a client (Raspberry Pi).
The communication protocol, seems like AT commands, in modem communication.
All data are exchanged in ASCII format. No binary chars are transmitted or received (except for the control chars from 0x00 to 0x1F.