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

When the optional cycle steal (CS) feature is installed in the 5010 Processor Module,however, the system can operate with a 5022 Disk Storage Module (also equipped withthe cycle steal feature) in a mode known as cycle stealing. This is a method of datatransfer (up to 3,072 words with a single I/O instruction) that significantly reducesprocessor load and response time required to handle data transfers. I/O operations areoverlapped with processing operations so that processing operations can continue whileI/O operations are in progress.Any model of the processor module may accommodate the CS feature which allowsdirect access to storage, through the channel, by an I/O device (for example, the diskstorage module).The order of priorities in the CS feature is tailored to a process control environment.As such, priority in the channel is assigned as follows:1. Top priority to the presentation of interruptions to the processor.2. Secondary priority to execution of I/O commands, or polling for interruptionsfrom modules and servicing CS requests. Executing commands and polling do notoccur at the same time.This order of priorities allows maximum system response to interruption conditions,but CS response capability is sacrificed to do this. Thus, if a nonbuffered subchannel iscontrolling a synchronous I/O module, (for example, a 5022 Disk Storage Module)during periods of high channel loading, a data service overrun may occur. This happenswhen the module's request for service exceeds the channel's capability to provideservice.In a typical operating environment, overrun conditions should be extremely rare. Ifthey do occur, however, comprehensive status is provided to allow recovery.Cycle steal operations between the processor module and the disk storage module aredescribed in Chapter 15.I/O ModulesI/O modules are physical structures housing the total logic and signal processing functionsfor I/O devices. Each I/O module connects to the processor through the system internalinterface and channel. These I/O modules are:• IBM 5014 Analog Input Module• IBM 5012 Multifunction Module• IBM 5013 Digital I/O Module• IBM 5022 Disk Storage ModuleLogic contained within an I/O module is divided into two parts:1. Common controls.2. Device logic and special controls that vary depending upon the type of I/O device.The common control logic governs data transfers between the I/O modules and theprocessor module. Device logic and special controls govern data transfer between the device(for example, analog point, digital group, disk file) and the common control logic.Sensor-Based ModulesThe IBM 5014 Analog Input Module is available in 5 models (models B1, Cl, D1, El andE2). Each model can have as many as 128 analog input points, but they operate at differentscanning rates (number of points scanned per second). Each model is described morefully later in this manual.The IBM 5012 Multifunction Module may contain the following features:• As many as 32 analog input points. All points must be of the same speed. Performanceof the analog input feature in this module is identical to that of the IBM 5014 AnalogInput Module (models Bl and C1).