ASCII CODE
ENQ
https://en.wikipedia.org/wiki/Enquiry_character
ENQ is a 0x05 or Ctl-E. ENQ is used in point-to-point or multi-point communications protocols. One terminal or computer sends an ENQ which is an inquiry to the other terminal asking if is it ready to receive data. The usual response is ACK (0x06 or Ctl-F), an "acknowledgement" that it's ready to receive.