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IBM S/360-370 IO Instruction Format. Base Add. Displacement Add. 0. 16. 20. 31. Instr: START IO, HALT IO and TEST IO - Available - busy, not operational - interrupt pending. B. D. IOP and IO Device addr. OPcode. Executed by CPU. 0. 8. 63. 32. 37. 48.
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IBM S/360-370 IO Instruction Format Base Add Displacement Add 0 16 20 31 Instr: START IO, HALT IO and TEST IO - Available - busy, not operational - interrupt pending B D IOP and IO Device addr OPcode Executed by CPU 0 8 63 32 37 48 Absolute memory address Flags Data count (bytes) Opcode Executed by IOP :channel command words
Channel command words • IO instru executed by the IOP. • Three main types: • Data transfer: input, output and sense. These CCWs cause the number of bytes specified in the data count field to be transferred betw the specified main memory region and the previously selected IO device. • Branch instruc.: causes the IOP to fetch next CCW from the specified memory location rather than sequential location. • IO device control: these instructions are transmitted directly to the IO device; dev. Specific. not involved in data transfers.
CPU Prog IOP Prog CPU-IOP comm. region IOCR System bus DMA Req CPU IOP DMA ACk INT req Attention IO Bus . . . IO dev IOP Organization • IOCR • CPU can place parameters of an IO task, e.g. address of the IO program to be executed and the IO device identity. • Standard DMA operation • CPU can attract IOP’s attention by ‘Attention’ line when executing TEST IO or START IO instruction. • IOP can also attract CPU’s attention by INT request line.
