Generalities
Two types of bus connect the adapters to the CCU/SCTL.
1. IOC bus: This bus connects the CCU to the adapters.
2. DMA bus: This bus connects the SCTL card to the FESH and EAC cards. See
“DMA Bus” on page 3-10.
IOC Bus
Data, address, and control information exchanges take place between the work reg-
isters and adapters attached to the IOC bus.
The IOC logic operates differently depending on whether the program initiates an
operation (PIO), or the adapter initiates it (AIO).
In both operations, the A (address) and D (data) registers of the data flow con-
trolled by the IOC logic act as buffers between the CCU(s) and the adapters (CAs
and LAs).
The IOC bus carries interrupt requests from the adapters (levels 1, 2, and 3) when
not busy with PIO or AIO operations.
IOC Bus Protocol
Read PIO example
│
┌─────────────────────────────────────────┐
│
│ IO Line
│
│
───┘
└───
│
│
┌───────┐
│
│Out Tag│
│
───────┘
└─────────────────────────────────
│
│
┌───────┐
│
│ TA Tag│
│
───────┘
└─────────────────────────────────
Control │
%
┌───────┐
Lines
│
│ TD Tag│
│
──────────────────────────────────┘
└──────
│
│
┌───────┐
┌───────┐
│
│ Valid │
│ Valid │
│
──────┘ HW
└───────────────────┘ HW
└──────
│
│
┌───────┐
│
│ Parity│
│
──────────────────────────────────┘ Valid └──────
Data
│
┌───────┐
┌───────┐
%
│IO Add/│
│ Data
│
Lines
│
──────┘Command└───────────────────┘ HW
└──────
3-4
IBM 3745 Models 130, 150, 160, 170, and 17A: Hardware Maintenance Reference
Summary of Contents for 3745 Series
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