Abstract: A microprogrammable peripheral controller in addition to being operative to controlling plurality of input/output devices in response to commands for processing information signals from a magnetic medium also includes apparatus for independently establishing a minimum operating capability within the controller. The apparatus includes a read-only control store arranged to store microinstructions and a limited number of basic bit patterns. The apparatus in response to an external control signal is operative to condition the data recovery apparatus included in the controller to receive the blocks of synchronization and data patterns arranged in a predetermined format and generated from basic bit patterns obtained from the control store. Simultaneously therewith, the apparatus inhibits normal transfer of information from the magnetic medium.

Abstract: A magnetic tape subsystem includes a peripheral controller which processes data signals of a block received during the reading and recording of the block on a magnetic tape medium by a selected one of a plurality of magnetic tape devices in response to commands received from a data processing system. The peripheral controller includes a data recovery unit having a plurality of storage indicators. These indicators are set by the controller in accordance with the characteristics of the block of data signals recovered by the data recovery unit providing indications of the results of the reading or recording operation performed by the selected magnetic tape device during the peripheral controller's execution of the command. The controller divides up the interval of time of an operation into a number of time periods and monitors the characteristics of the signals of a block which should be received by the data recovery unit during those intervals.

Abstract: A microprogrammed control for a controller operates with an instruction set which includes a pair of microinstructions, each having an op code field. One of the microinstructions has an op code field coded to specify a load constant operation in which a constant field of the microinstruction is loaded into an auxiliary register coupled to the control store of the microprogrammed control. The other microinstruction has an op code field coded to specify an unconditional return branch operation to a location specified by the contents of the auxiliary register loaded previously. Pairs of these microinstructions arranged in a predetermined sequence are included within each routine of microinstructions stored in the control store which the controller is required to execute in parallel.

Abstract: A microprogrammed peripheral controller in response to a command executes a sequence of microprogram routines stored in a read only memory normally provided for execution of peripheral control commands, based upon the state of various status indicators included in the peripheral controller. The controller automatically executes only those microprogram routines required to accomplish a given operation in the correct sequence by employing operation phase code bits stored in a scratch pad memory. The code bits are updated after execution of each microprogram routine and upon being changed to a predetermined state signal the controller when the given operation has been completed.