[chirp_users] VX-170 download but no upload

I am able to download from the VX-170 but not upload. I take it that the same "clone" mode is used for download and upload. I note that the data for Rx and Tx go through the same pin on the 4 pin yaesu connector. I assume that the Rx and Tx data alternate on the same line because it is shared. Question: When uploading to the radio , does the software need to Tx and Rx to/from the PC to the radio or does it just Tx from PC to radio ? ie is there handshaking involved or just a steady transmit stream from the PC to the radio? tnx Mike VE7SML