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Priority System for Communication Control Unit Disclosure Number: IPCOM000074594D
Original Publication Date: 1971-May-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 3 page(s) / 42K

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Related People

Maholick, AW: AUTHOR [+3]


The described system relates to a multiplexor for communication lines and more particularly to a priority system.

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Priority System for Communication Control Unit

The described system relates to a multiplexor for communication lines and more particularly to a priority system.

This priority system provides a combination of two priority schemes by classifying the I/O devices of a system into groups of devices, each group having substantially similar priority needs and by giving each group a priority according to its needs. Within a group, priority will be assigned on a time basis with the first ready device being serviced when its group has first priority of the groups needing service. An address register is provided for each group of I/O devices and when a device is found to require service, its address is stored in its group register and a service request signal is sent to interrupt the processor. The processor will then scan all the address registers and service, in order of priority, the devices whose addresses are stored. The address registers are rescanned each time one device is serviced and if a high-priority device asks for service while a lower-priority device is being serviced, its request will be taken up as soon as the action for the lower-priority device is completed even though other low-priority devices have been waiting longer.

The preferred embodiment of the multiplexor is as shown. The multiplexor is attached to one channel of a host central processing unit (CPU) by Bus In 20 and Bus Out 21, which connect to channel adapter section 23. The channel adapter responds to all of the control signals on the channel busses and appears as a single control unit using a single-channel address. All information to and from the channel through adapter 23 is monitored by central control unit (CCU) 24 which contains the circuits and data flow paths to control main storage 25, local storage registers channel adapter 23 and disk adapter 27 connected to disk file 130. The CCU 24 operates under control of routines stored in main storage 25 to implement the multiplexor functions. One or more communication scanner bases (CSB) 28 are attached to CCU 24 to scan up to five line-interface bases 29, each of which can provide service for a group of communication lines 31 through conventional line adapters 32. The primary function of CSB 28 is to periodically scan the hardware in li...