Help and 1k Xmodem Protocol implementation (go pick) Is a PC with a dial-up modem modem protocol widely used in asynchronous communication file transport protocol. Standard Xmodem and 1k-Xmodem divided into two, which transmit data in 128-byte blocks, which 1k a block of bytes or 1024 bytes, and supports the General calibration both CRC and and validate, in the event of a data packet error supports multiple retransmissions (generally 10 times).