Abstract: Described is an architecture and protocol for exchanging messsages within a distributive data processing system. Instead of transmitting a frame with a beginning flag field (SDEL) followed by an address field as is the usual case, the SDEL field and address field collapsed and merged into a single field. The field includes a control bit whose setting determines whether the field is the beginning of a frame or otherwise. A second control bit within the single field is used to identify the type of message being transmitted and the response that a recipient station is permitted to return to a control unit issuing the message. The protocol is well suited for framing messages in the well known SDLC communications format. In this format it allows the detection of delimiters without resorting to bit stuffing.

Abstract: In a data transmission system comprising of a transmitting unit, a plurality of remote devices, and one or more serial communication links interconnecting the devices to the transmitting unit the polarities of a serially transmitted test signal and a locally generated control signal are used to provide unique addresses for identical devices connected to the transmitting unit. The technique provides a dynamic scheme for assigning addresses to identical devices.

Abstract: A printed circuit board holder includes an integral, generally rectangular board receptacle which is pivotally supported above the base of a data processing device by spaced cradle posts. The receptacle can be pivoted from a normal position through an angle of approximately 90.degree. to a service position in which the receptacle bottom wall is nearly perpendicular to the base. An integral latch mechanism keeps the holder in the normal position until the latch is manually released. Multiple pin connector boards and stiffener plates are secured to the receptacle by integral latches.

Abstract: A digital data communication network in which half-duplex communications are established between a central station and a plurality of remote terminal devices under control of the central station and in which said remote terminal devices are grouped and each group is serially connected and receives data signals in parallel over a simplex link from the central station and in which one group of serially connected stations is selectively connected to a second simplex link for transmitting, in a predetermined sequence, data signals to the central station.