Abstract: A communications system employs a multiline bus including control lines for multiple functions in order to minimize the required number of bus lines. This technique is most applicable to small computer systems which are hand portable or briefcase portable and which operate with small peripherals. The transmitting device places an active signal on a handshake line for a predetermined period of time. The receiving device detects this active signal and also places an active signal on the handshake line. The transmitting device applies valid data to the data lines throughout the period that a active signal is on the handshake line. Upon detection of the data the receiver releases the handshake line. Using this technique a single line is used to indicate valid data transmission and proper reception. An additional bus available line, used by a master device to alert slave devices that communications are in process, can be employed by at least some of the slave devices to request service from the master device.

Abstract: A data processing apparatus capable of operating in a plurality of modes includes a technique for automatically determining the proper mode from user inputs. This invention is most applicable to small hand held or desk top data processing apparatuses which operate in one mode like a calculator and which include provisions for entering, editing and running computer programs in a higher order language. User inputs, such as those from an ordinary keyboard, are stored in an input buffer memory until an end-of-entry key is actuated. Depending upon the nature of the end-of-entry key and the particular set of keyboard entries stored in the input buffer memory, the apparatus automatically determines the required mode for processing the data in the input buffer, enters that selected mode and peforms the function required by the input characters.