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20:20 Channels
General Description
support processor. The scan-in and scan-out functions are used to transfer data
between the two components, for example, data or programs read by the support
processor from a diskette drive (such as the TEST BLOCK internal records, 1/0
configuration data set, and Input/Output Configuration Program). In 4341
Processors, the local channel adapter interface is used for such communication.
In addition, the 4381 instruction processing function can set an interrupt for the
support processor to indicate its services are needed (for example, a state change
occurs, such as a machine check that requires a scan-out). This eliminates polling
by the support processor, as is done in 4341 Processors.
Communication between the operating system and the operator (via the operator
console) is handled via the local channel adapter in 4381 Processors, as in 4341
Processors. However, since the local channel adapter is not used for
communication between the instruction processing function and the support
processor, communications problems between these components that can arise in a
4341 Processor when channel 0 is in a hung condition do not arise in a 4381
Processor.
The 43 81 Processors implement advanced channel functions like those
implemented in 4341 Processors, such as block multiplexing and data streaming,
and also offer more channels and higher aggregate channel data rates than do 4341
Processors.
One standard and one optional channel group are provided for all uniprocessor
4381 model groups. The standard channel group consists of one byte multiplexer
channel, addressed as channel 0, and five block multiplexer channels, addressed as
channels 1 through 5. Channel 5 can be configured as a byte, instead of a block,
multiplexer channel. The optional channel group (Block Multiplexer Channels,
Additional feature) provides six block multiplexer channels addressed as channels 6
through B.
A byte multiplexer channel in a 4381 Processor can handle the concurrent
operation of multiple slower speed devices when operating in byte interleave mode,
while a block multiplexer channel can support interleaved, concurrent execution of
multiple high-speed channel programs.
Each installed byte or block multiplexer channel can have up to eight control units
attached. For byte multiplexer channel 0, one control unit position is used by the
local channel adapter. This internal adapter provides attachment of support
processor subsystem devices to this byte multiplexer channel. As a standard
feature, automatic control unit powering is provided for up to 32 control units
attached to a 43 81 Processor.
Comprehensive error checking is incorporated in the basic design of the channel
hardware. Checking is performed on the control logic in most areas, and standard
Section 20: 4381 Processor Uniprocessor Model Groups
4 7
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