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

I/0 Command FunctionsImmediate Write (Fun=001)An immediate write command transfers one word (16 bits) of data from a specifiedprocessor register to the addressed device. The result indicators are not changed.Immediate Read (Fun=010)An immediate read command transfers one word (16 bits) of data from the addresseddevice to a specified processor register. The result indicators are changed to reflect thefinal contents of the specified register.Prepare I/O (Fun=011)The prepare I/O command transfers one word (16 bits) of data from a specified processorregister to the addressed device. The difference between this command and the immediatewrite command is the data and its purpose. The immediate write command transfers datafor transmission to the output device or point, or for control of attached I/O devices. Theprepare I/O command transfers information advising the device whether it is allowed tointerrupt and, if so, on what priority level and sublevel.The data sent to the device by the prepare I/O command has the following format andmeaning:0 4 8 15Level Sublevel Zeros00XX X XX X 0 0 0 0 0 0 0 XI I 1 I I 1 I I I I I I0-3 0-F 0 0 or 1The significance of the data fields in this word are described as follows.Level: This 4-bit field specifies the priority interruption level assigned to the interruptingsource. The binary value of bits 2 and 3 indicates the priority level (0, 1, 2, or 3). Bits 0and 1 must be 0.Sublevel: This 4-bit field assigns a sublevel (from 0000 to 1111) to the interruptingsource. When requesting an interruption, the source presents this sublevel so that thesystem can locate the starting address of the servicing routine in the appropriate leveltable. A sublevel of 0000 accesses the second word in the table; a sublevel of 1111 accessesthe seventeenth (last) word. The first word in each level table is reserved for the oldinstruction address associated with a program check interruption. (Refer to Chapter 3,"System/7 Interruptions," for more detail.)Zeros: This field is not used, but its value must be set to 0.I. This bit determines whether the device is allowed to request an interruption. An I-bitvalue of 1 permits the device to request an interrupt, and a value of 0 prevents it. (Theinterruption mask determines whether the device can actually interrupt the processor.)If the device is not permitted to cause an interruption, issuing an interruption-causingcommand results in:1. Condition code 1 being set.2. The command reject indicator being set in the DSW.3. The command not being executed.The prepared device stores the PIO data and presents the priority level and sublevelto the processor each time the device presents an interruption request (and interruptionsare enabled). Data stored at the device is reset on a system reset, a power-on reset, or change(by the successfu' execution of another prepare I/O command to the device.Processor Instructions 4-57