Systems Reference Library - All about the IBM 1130 Computing ...

Page of GA26-5918-8Revised July 14, 1971By TNL: GN26-0269Input/Output ControlInput/output (I/O) operations transfer informationbetween core storage and I/O devices. Input/outputdevices include card read punches, magnetic tapeunits, disk storage devices, printer-keyboard devices,printers, plotters, communications devices,and process control equipment. The 1800 also hasfeatures that are internal to the processor-controller(P-C) but are considered I/O devices by the program.These features include the P-C console, theinterval timers, the operations monitor, and theinterrupt mask register.I/0 device operations are controlled by adapters.Each I/O device has its own adapter. Thisadapter may be separate from the I/O device orincluded as an integral part of the I/O device. Forexample, the 1443 Printer has a separate adapter;the 1810 Disk Storage contains its own adapter. Inany case, the adapter provides the logical and bufferingcapabilities needed to operate its specificI/O device. From a programming point of view,most adapter functions merge with I/O device functions.With the exception of internal I/O devices, eachI/O device adapter has standard signal connectionsto the P-C and responds to a standard set of signalsfrom the P-C. This "I/O unit to P-C" connection iscalled the I/O interface. It enables the P-C to controlall I/O operations with a common set of instructions.INPUT/OUTPUT CONTROL COMMANDSThe 1800 system uses the execute I/O (XIO) instructionto control all I/O operations. The effectiveaddress (EA) of the XIO specifies the core storagelocation of a two-word input/output control command(IOCC). The IOCC specifies the device to be selected,the function to be performed with the selecteddevice, and if necessary, the core storage locationassociated with information sent to or received fromthe selected device.Execution of the XIO instruction causes theIOCC to be read from core storage and the functionspecified is performed on the selected device. Thebasic format of an IOCC is shown in the followingillustration.0 15 0 4 8 15Area1 1 I 1 II 1 I 1 1 k 1 1Area Function Modifier j115708The five-bit area field specifies the device to beused in the I/0 operation. In some cases, the areacode may represent a group of devices, such asmagnetic tape units or printer-keyboards. In thesecases, the modifier field specifies the particulardevice within the group.Area codes are preassigned to each type of I/0device that can be ordered for the 1800 system. Alist of these devices and their respective area codesis shown in Figure 12.FunctionAddressEven Location(EA)Odd Location(EA+1)The three-bit function field specifies the primaryfunction or operation to be performed. Eight primaryI/O function codes are provided; these areexplained next.000 -- CUSTOMER ENGINEERING (CE) MODE:This function code is used to remove some I/0 devicesfrom on-line status and place them in CEmode, or vice versa.001 -- WRITE: This function code causes a singleword to be transferred from core storage to an I/Odevice. The core storage location of the single wordis specified by the IOCC address word. The currentcontents of the accumulator are destroyed by executionof a write function. It is the programmer's responsibilityto save the accumulator contents, ifnecessary.010 -- READ: This function code causes a singleword to be transferred from an I/0 device tocore storage. The core storage location isspecified by the IOCC address word. The currentcontents of the accumulator are destroyedby execution of a read function. It is theInput/Output Control 53