enquiry (control character) (ENQ)
Inquiry (ENQ), request, is a transmission control character (TC5) in character-oriented protocols such as Binary Synchronous Communication( BSC) or Medium Speed Version( MSV) with central control.
The ENQ character is used by the central station (master station) to request the peripheral data stations ( slave stations) to send (poll) or receive data. The transmission control character ENQ from the IA-5 alphabet is used to request a response from a remote station.
Further for repeating an acknowledgement as well as requesting the utilization of a block. In the ASCII character set, ENQ has the ASCII value 005.