Teoria

ECR17 is a request-response protocol between an Electronic Cash Register and an EFT-POS terminal. The cash register sends a command frame, the terminal acknowledges transport-level receipt, performs the requested operation, and returns an application result frame.

Frame families

LRC

The implementation starts from base 0x7F and XOR-folds the configured bytes.

For a byte sequence (b_1, b_2, \ldots, b_n):

lrcMode controls whether STX and ETX participate in that fold:

• stx: STX + payload + ETX
• std: payload
• noext: payload + ETX
• stx_noext: STX + payload

Timing

The session uses distinct timeouts for connection, ACK, and final response. Separating them helps identify whether the failure is the LAN socket, terminal handshake, or host-side transaction wait.