Abstract: An apparatus and method wherein a switching means, which has the capability of generating one of a number of different output selection signals, is set to an automatic mode or a non-automatic mode. In the automatic mode, the switching means automatically switches from generating one selection signal to another selection signal in response to a predetermined input which includes a control pulse. In the non-automatic mode, no such switching occurs. In addition, the apparatus generates a pseudo-control signal which, in the non-automatic mode only, changes in a predetermined manner in response to the control pulse so as to simulate the control pulse. According to a preferred embodiment, the above functions are performed by a switchover circuit which is employed in a multi-tape well logging system to automatically switch from one tape to another tape upon reaching an end of tape.

Abstract: A serial line communication system is provided whereby a plurality of remote units are tied to a central site through a serial communication line. Each remote unit is provided with an automatic bit rate detection means. Messages returning from the remotes are checked at the central site for errors. If errors occur, the central site automatically retries to achieve error-free communication. If necessary to achieve error-free communication, the central site is provided with means for automatically shifting to a lower secondary bit rate to achieve communications with a particular remote. The central site then shifts back to the higher primary bit rate for communication with the next remote.

Abstract: In a computer system in which address lines and data lines are utilized to interface bus devices to the computer, data is provided to the computer from nonaddressable switches by connecting at least a portion of the data lines to ground through a pull-down resistor and to a positive voltage through a switch and a pull-up resistor. Depending upon the position of the switches associated with each data line, each data line will be pulled to a high logic level or a low logic level when the data lines are in the tristate high impedance mode. The computer can read the contents of the switches even though the switches have no associated address decoding or bus driving circuitry.

Abstract: A serial line communication system is provided whereby a plurality of remote units are tied to a central site through a serial communication line. Each remote unit is provided with an automatic bit rate detection means. Messages returning from the remotes are checked at the central site for errors. If errors occur, the central site automatically retries to achieve error-free communication. If necessary to achieve error-free communication, the central site is provided with means for automatically shifting to a lower secondary bit rate to achieve communications with a particular remote. The central site then shifts back to the higher primary bit rate for communication with the next remote.

Abstract: Control of the data format programmed into an interface means by a computer means is provided in response to the data format required by an I/O device. A register in the interface means is programmed to respond to only a first digital address from the computer means. A switching means having first and second positions is utilized to create "don't care" positions in a digital address from the computer means to the interface means. Because of the "don't care" positions in the digital address the register in the interface means will respond to a second digital address when the switching means is in the first position. The register will not respond to the second digital address when the switching means is in the second position. When the register responds to the second digital address then the computer programs the data format required by a first I/O means into the interface means.