IBM System/7 Functional Characteristics - All about the IBM 1130 ...

1111111111111111111111■11•11111111111111111111111111111A general DSW has the following format, with modules providing the bits pertinent totheir operation. (Bits not used by the module are set to 0.)Significant Bits Meaning1 Command reject. The addressed module cannot execute thecommand issued. An example is an interruption-causingcommand issued to a device disabled for interruptions.3-7" Device dependent. (See individual devices.)14 Data check. A parity error involving data is detected on theinterface. The operation that caused this condition can usuallybe retried successfully if the error condition is intermittent.This error bit does not apply to the DSW for the processor modulebecause the machine check interruption performs this function.15 Invalid device address. This bit is set on if the point, group, ordevice is not available to the system. (This bit does not apply toall I/O modules.)Any error encountered during an immediate read DSW or read ISW is recorded in theDSW, replacing the original contents, and setting the condition code to 1.Interrupt Status Word (ISW)The 16 bits in the ISW are set when errors are detected after completion of immediate I/Ocommands and while the device is busy. Normally, any ISW bit set on (except thedevice-busy bit) causes the device to present an interruption request. Each interruptingdevice in a module has its own ISW.An ISW can be read by the immediate read ISW command. If this instruction is successfullyexecuted, the ISW is reset provided its interruption request has been accepted by thesystem. The ISW is also reset by halt I/O, system reset, or the first new selection ofthe device by a command (except immediate read ISW) after a pending interruption fromthe device has been accepted by the system.The read ISW command is described for each interrupting source in the respective chaptercovering that device or module.A general ISW has the following format, with the interrupting sources providing the bitspertinent to their operation. (Bits not used by the interrupting source are set to 0.)Significant Bits Meaning0 Attention. The device has detected an external condition that issignificant to the program. The condition is interpreted by theprogram and is not associated with the initiation, execution, ortermination of an I/O operation. If the device is busy or has aninterruption pending, the attention bit will be presented with theinterruption that occurs later when the device becomes not busy.Otherwise, an attention condition will cause the device to requestan interruption.2 Overrun. A device requires data servicing beyond the capability ofthe system to accept data. This bit may or may not be consideredan error bit, depending on the use of the bit within the I/O module.3-7 Device dependent. (See individual devices.)12 Device busy. The device is working, either busy or waiting for aninterruption to occur.13 Device end. The device has terminated an operation in a normalmanner. This is not an error condition.15 Device dependent. (See individual devices.)