Patent GB-1306473-A (GB)
Title: Terminal units for use at a remote station of a data transmission system
IPC: G06Q20/40
Filed: 1971-04-19
Abstract: 1306473 Selective signalling; checking credit accounts DATA CARD CORP 19 April 1971 [11 March 1970] 23605/71 Headings G4H and G4T A terminal unit includes a memory into which information can be entered and dial means for establishing a transmission channel to a central station, establishment of the channel causing read out of the stored information and transmission of it as a coded enquiry message to the central station, the channel being disconnected and the stored information being cleared if a reply is not received within a predetermined time, there being reply detection means responsive to the contents of the reply message (if received) for visually conveying information from the central station.  A credit verification terminal unit has manual keys and manual sliders to respectively enter the account number (which may be a credit card number) and the purchase amount into a store, the contents of a normal/hold switch and a purchase/refund switch also being entered. Pressing a send key causes an automatic dialler to acquire a telephone channel link to a central station, resulting detection of a carrier tone at the terminal unit, in conjunction with the operated state of the send key, starting a timer and also causing a scanner to scan the memory and send its contents as an enquiry message to the central station. The message includes (besides the information entered into the store, see above) a unique start character (to preclude use of the system by unauthorized equipment), an identification of the type of terminal unit (viz. credit, since the central station may also be fed from burglar and fire detector units), the identity number of the particular terminal unit, a check digit equal to the number of 1 bits (or 0 bits) in the message (excluding this digit and the end of message character), and an end of message character, most of this being permanently stored in the store. Each character in the message may also have a parity bit. The central station determines the credit status from a memory and sends a reply message back which is decoded if valid to light one of three lamps " OK ", " NO " and " ? ". If the " OK " lamp is lit an imprinter carriage is unlocked (see below) and an authorization counter is advanced. The timer mentioned is stopped if the reply is valid (parity check) but otherwise the timer will subsequently time out (as it will if there is no reply) and light an " error " lamp. Alternatively the invalid indication may light this lamp directly. An imprinter region of the terminal unit has a platen for receiving a credit card (to permit an embossed credit card number to be printed), a user platen (to permit the user identity to be printed), and print wheels variously actuated by the manual sliders (to print the purchase amount) and associated with the authorization counter and for the date. When the imprinter carriage is unlocked it can be moved manually across the imprinter region to cause the aove information to be printed on a sales slip. The original operation of the send key locked the manual sliders. Unlocking, clearing and resetting in the terminal unit are described as is hanging up the telephone connection. For example, reception of a valid reply message hangs up the connection if the normal/hold switch is at " normal " but not if it is at " hold ". Hang up also occurs if the timer times out, and also if the carrier tone is not detected. Detection of the carrier lights an " on-line " lamp.