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Browse Prior Art Database

Scan Controlled Device

IP.com Disclosure Number: IPCOM000049801D
Original Publication Date: 1982-Jul-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

Kim, YM: AUTHOR

Abstract

This invention relates to a network invoked by the powered-down state of a counterpart device in a chain such that a signal propagating there through the chain will bypass the off device. A selection signal is impressed upon a group of devices in parallel with the result that the network passes the signal serially in a chain of priority order.

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Scan Controlled Device

This invention relates to a network invoked by the powered-down state of a counterpart device in a chain such that a signal propagating there through the chain will bypass the off device. A selection signal is impressed upon a group of devices in parallel with the result that the network passes the signal serially in a chain of priority order.

The network includes a scan ring, shown in Fig. 3, which is of the shift register type. Each shift register output is priority assigned in the order of "a" through "h". Scan path 1 provides the signal path connection for either "Pah" or "PAH". A "Pah" is the signal from the output of "a" with the highest priority. It is gated by the propagate select out signal from the selection logic, as seen in Figs. 4 or Each output will go to a corresponding selection logic.

The dotted output, ahPah or AHPAH, is coupled to a scan clock input.

Scan path 2 as seen in Figs. 5 and 9, provides signal indication of the end of a scan in a chain. The dotted output, jah or JAH, drives the input of the scan clock and inhibits the clock at the end of the scan. Parenthetically, the scan clock, as seen in Figs. 6 and 10, is of the edge-triggered JK flip-flop type. The level of either scan path 1 or scan path 2 will be clocked by T0, control unit clock, regulating the clock input to the scan ring.

Fig. 1 shows a control unit coupling a CPU-driven channel to a serially reuseable device. In Fig. 2, the channel sends a select out...