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

The prepare I/O command is used as described in Chapter 4 under "Input/OutputInstruction." Only three device addresses are used with the prepare I/O command inorder to prepare an input source to interrupt. The three device addresses and theirfunctions are:Device AddressFunction000000 Prepare digital input group 0 with process interrupt feature000100 Prepare digital input group 1 with process interrupt feature100000 Prepare 2790 ControlDIGITAL INPUT CONTROLThe digital input control function of the digital I/O module can accommodate as manyas 128 isolated and/or non-isolated digital input points, in eight groups of 16 pointseach. These points are two-terminal inputs that can be activated by either contact orvoltage sources provided by the user's equipment. A non-isolated digital input groupprovides 16 latching or non-latching points of contact sensing capability.A digital input contact point has a 1 value in its corresponding bit when the contact isclosed, and a 0 value when the contact is open.An isolated digital input voltage point has a 1 value in its corresponding bit when theinput is from +2V to +52.8V, and a 0 value when the input is from —52.8V to +0.6V. Anon-isolated digital input voltage point has the opposite polarity sensing; a 0 value from+2V to +52.8V, and a 1 value from —52.8V to +6.0V. An input between +0.6V and +2V,in either case, produces an indeterminate result.Each group of digital input points can be program controlled to provide either latchedor unlatched input. In the latched mode of operation, each bit that is set on in the groupremains in that state (regardless of any further change in input signal or contact operation)until the group is reset or unlatched. A bit is not reset if the input signal remains active(voltage present or switch closed) throughout the execution of the read/reset digital inputregister command. In the unlatched mode of operation, each bit in the group is set on oroff dynamically as determined by the input fluctuations.Digital input circuits are compatible with digital output circuits, which permitsmultiplexing of digital output points with the user's contacts for digital input sensingapplications. If all of the points are isolated, either positive or negative voltagesources can be used through proper connection of input sources to the input terminals.This circuit compatibility also permits direct connection of digital input points todigital output points for testing of the input/output circuits.Process Interrupt FeatureA Process Interrupt feature can be obtained for one or both of the first two digital inputgroups (group 0 and/or group 1). Each of the two groups is a separate interrupting sourceand, therefore, can be assigned its own priority level and sublevel by separate prepare I/Ocommands. Group 0 is installed when only one group is ordered. The Process Interruptfeature can be attached only to isolated groups.With the Process Interrupt feature, a 16-point group is compared with a 16-bit referenceregister (which can be set to any value by the program), and an interruption request ispresented on the basis of either an equal or an unequal bit-by-bit comparison. The choiceof comparison is under program control and can be changed at any time. When a grouphas been conditioned to perform a compare operation, the program cannot read the digitalinput register for that group until an interruption request is presented. After the requestis presented, the group will no longer be conditioned to perform a compare operation.The group can then be used the same as a noninterrupting digital input group.14-4 GA34-0003