Bus grant line - Revision history

Jnc: Mention the race between a new request and an old grant; add clarification about basic operation

2025-07-27T17:03:15Z

Mention the race between a new request and an old grant; add clarification about basic operation

Jnc: /* See also */ +UNIBUS/QBUS DMA lines

2023-02-13T23:01:02Z

‎See also: +UNIBUS/QBUS DMA lines

Jnc: /* See also */ +M8264 No-SACK Timeout Module

2022-12-04T14:27:29Z

‎See also: +M8264 No-SACK Timeout Module

Jnc: +see also

2019-10-01T17:37:26Z

+see also

Jnc: +cat

2018-12-16T00:08:47Z

+cat

Jnc: +link

2018-09-18T18:30:08Z

+link

Jnc: Discuss priority

2018-09-18T15:34:26Z

Discuss priority

Jnc: Simpler

2018-01-06T01:02:49Z

Simpler

Jnc: Add grant continuity cards

2018-01-05T12:33:43Z

Add grant continuity cards

Jnc: Separate page for use by other pages

2017-07-23T14:50:34Z

Separate page for use by other pages

New page

'''Bus grant lines''' are used in a number of bus architectures (for example, the [[UNIBUS]] and [[QBUS]]) for the [[CPU]] to communicate to devices that their request for [[interrupt]]s and [[Direct Memory Access|DMA]] have been granted (hence the name).

They are wired in series, so that one device's 'grant out' line is connected to the next device's 'grant in' line, starting the the CPU's 'grant out' line. When a device sees a 'granted' pulse on one of its grant in lines, '''if''' the device had requested a DMA/interrupt, it 'consumes' the grant pulse, and goes on to do the type of operation it requested; if it was '''not''' requesting that type of operation, it 'passes' the grant by generating a 'granted' pulse on '''its''' grant out line.

@@ Line 1: / Line 1: @@
-'''Bus grant lines''' are used in a number of bus architectures (for example, the [[UNIBUS]] and [[QBUS]]) for the [[Central Processing Unit|CPU]] (or whatever circuitry is controlling the bus) to communicate to [[device controller]]s that their request for [[interrupt]]s and [[Direct Memory Access|DMA]] have been [[bus grant|granted]] (hence the name).
+'''Bus grant lines''' are used in a number of bus architectures (for example, the [[UNIBUS]] and [[QBUS]]) for the [[Central Processing Unit|CPU]] (or whatever circuitry is controlling the bus) to communicate to a [[device controller]] that its request for an [[interrupt]] or [[Direct Memory Access|DMA]] has been [[bus grant|granted]] (hence the name). The CPU does this by sending a [[pulse]] down the grant line, to the device controller, to notify it.
-They are often wired in series, so that one device's 'grant out' line is connected to the next device's 'grant in' line, starting the the CPU's 'grant out' line. When a device sees a 'granted' pulse on one of its grant in lines, '''if''' the device had requested a DMA/interrupt, it 'consumes' the grant pulse, and goes on to do the type of operation it requested; if it was '''not''' requesting that type of operation, it 'passes' the grant by generating a 'granted' pulse on '''its''' grant out line.
+Such lines are usually wired in series, so that one device's 'grant out' line is connected to the next device's 'grant in' line, starting the CPU's 'grant out' line. When a device sees a 'granted' pulse on one of its grant in lines, '''if''' the device had requested an interrupt/DMA, it 'consumes' the grant pulse, and goes on to do the type of operation it requested; if it was '''not''' requesting that type of operation, it 'passes' the grant by generating a 'granted' pulse on its grant out line.
-In other words, when there are conflicting requests for the bus, this kind of system prioritizes the requests based on the devices' location on the bus; the ones closest to the CPU have the highest priority.
+(A perceptive reader may have noticed that there is a potential [[race]] here, between an incoming grant, previously sent by the CPU in response to some ''other'' device's request, and a ''new'' request just raised by the device. For a more detailed discussion of this topic, see [[Bus Arbitration on the Unibus and QBUS|here]].)
 On systems which have [[backplane]]s into which devices can be plugged, it is usually necessary to provide some means for a grant to 'jump over' an empty backplane slot; for the UNIBUS, this is done with either a [[G727 grant continuity card|G727]] or a [[G7273 grant continuity card]].
@@ Line 12: / Line 14: @@
 * [[DMA Request and Grant]] - QBUS DMA request and grant lines
 * [[M8264 No-SACK Timeout Module]] - in particular, the [[M8264 No-SACK Timeout Module#Functionality discussion|Discussion]] section
 [[Category: Hardware Basics]]

@@ Line 9: / Line 9: @@
 ==See also==
 * [[M8264 No-SACK Timeout Module]] - in particular, the [[M8264 No-SACK Timeout Module#Functionality discussion|Discussion]] section
 * [[Bus Arbitration on the Unibus and QBUS‎‎]]
 [[Category: Hardware Basics]]

@@ Line 9: / Line 9: @@
 ==See also==
 * [[Bus Arbitration on the Unibus and QBUS‎‎]]
 [[Category: Hardware Basics]]

← Older revision		Revision as of 17:37, 1 October 2019
Line 6:		Line 6:

	On systems which have [[backplane]]s into which devices can be plugged, it is usually necessary to provide some means for a grant to 'jump over' an empty backplane slot; for the UNIBUS, this is done with either a [[G727 grant continuity card\|G727]] or a [[G7273 grant continuity card]].		On systems which have [[backplane]]s into which devices can be plugged, it is usually necessary to provide some means for a grant to 'jump over' an empty backplane slot; for the UNIBUS, this is done with either a [[G727 grant continuity card\|G727]] or a [[G7273 grant continuity card]].
		+
		+	==See also==
		+
		+	* [[Bus Arbitration on the Unibus and QBUS‎‎]]

	[[Category: Hardware Basics]]		[[Category: Hardware Basics]]

← Older revision		Revision as of 00:08, 16 December 2018
Line 6:		Line 6:

	On systems which have [[backplane]]s into which devices can be plugged, it is usually necessary to provide some means for a grant to 'jump over' an empty backplane slot; for the UNIBUS, this is done with either a [[G727 grant continuity card\|G727]] or a [[G7273 grant continuity card]].		On systems which have [[backplane]]s into which devices can be plugged, it is usually necessary to provide some means for a grant to 'jump over' an empty backplane slot; for the UNIBUS, this is done with either a [[G727 grant continuity card\|G727]] or a [[G7273 grant continuity card]].
		+
		+	[[Category: Hardware Basics]]

← Older revision		Revision as of 18:30, 18 September 2018
Line 1:		Line 1:
−	'''Bus grant lines''' are used in a number of bus architectures (for example, the [[UNIBUS]] and [[QBUS]]) for the [[Central Processing Unit\|CPU]] (or whatever circuitry is controlling the bus) to communicate to [[device controller]]s that their request for [[interrupt]]s and [[Direct Memory Access\|DMA]] have been granted (hence the name).	+	'''Bus grant lines''' are used in a number of bus architectures (for example, the [[UNIBUS]] and [[QBUS]]) for the [[Central Processing Unit\|CPU]] (or whatever circuitry is controlling the bus) to communicate to [[device controller]]s that their request for [[interrupt]]s and [[Direct Memory Access\|DMA]] have been [[bus grant\|granted]] (hence the name).

	They are often wired in series, so that one device's 'grant out' line is connected to the next device's 'grant in' line, starting the the CPU's 'grant out' line. When a device sees a 'granted' pulse on one of its grant in lines, '''if''' the device had requested a DMA/interrupt, it 'consumes' the grant pulse, and goes on to do the type of operation it requested; if it was '''not''' requesting that type of operation, it 'passes' the grant by generating a 'granted' pulse on '''its''' grant out line.		They are often wired in series, so that one device's 'grant out' line is connected to the next device's 'grant in' line, starting the the CPU's 'grant out' line. When a device sees a 'granted' pulse on one of its grant in lines, '''if''' the device had requested a DMA/interrupt, it 'consumes' the grant pulse, and goes on to do the type of operation it requested; if it was '''not''' requesting that type of operation, it 'passes' the grant by generating a 'granted' pulse on '''its''' grant out line.

← Older revision		Revision as of 01:02, 6 January 2018
Line 3:		Line 3:
	They are wired in series, so that one device's 'grant out' line is connected to the next device's 'grant in' line, starting the the CPU's 'grant out' line. When a device sees a 'granted' pulse on one of its grant in lines, '''if''' the device had requested a DMA/interrupt, it 'consumes' the grant pulse, and goes on to do the type of operation it requested; if it was '''not''' requesting that type of operation, it 'passes' the grant by generating a 'granted' pulse on '''its''' grant out line.		They are wired in series, so that one device's 'grant out' line is connected to the next device's 'grant in' line, starting the the CPU's 'grant out' line. When a device sees a 'granted' pulse on one of its grant in lines, '''if''' the device had requested a DMA/interrupt, it 'consumes' the grant pulse, and goes on to do the type of operation it requested; if it was '''not''' requesting that type of operation, it 'passes' the grant by generating a 'granted' pulse on '''its''' grant out line.

−	On systems which have [[backplane]]s into which devices can be plugged, it is usually necessary to provide some means for a grant to 'jump over' an empty backplane slot; for the UNIBUS, this is done with either a [[G727 grant continuity card\|G727]] or a [[G7273 grant continuity card~~\|G7273~~]] ~~grant continuity card~~.	+	On systems which have [[backplane]]s into which devices can be plugged, it is usually necessary to provide some means for a grant to 'jump over' an empty backplane slot; for the UNIBUS, this is done with either a [[G727 grant continuity card\|G727]] or a [[G7273 grant continuity card]].

← Older revision		Revision as of 12:33, 5 January 2018
Line 1:		Line 1:
−	'''Bus grant lines''' are used in a number of bus architectures (for example, the [[UNIBUS]] and [[QBUS]]) for the [[CPU]] to communicate to devices that their request for [[interrupt]]s and [[Direct Memory Access\|DMA]] have been granted (hence the name).	+	'''Bus grant lines''' are used in a number of bus architectures (for example, the [[UNIBUS]] and [[QBUS]]) for the [[Central Processing Unit\|CPU]] (or whatever circuitry is controlling the bus) to communicate to devices that their request for [[interrupt]]s and [[Direct Memory Access\|DMA]] have been granted (hence the name).

	They are wired in series, so that one device's 'grant out' line is connected to the next device's 'grant in' line, starting the the CPU's 'grant out' line. When a device sees a 'granted' pulse on one of its grant in lines, '''if''' the device had requested a DMA/interrupt, it 'consumes' the grant pulse, and goes on to do the type of operation it requested; if it was '''not''' requesting that type of operation, it 'passes' the grant by generating a 'granted' pulse on '''its''' grant out line.		They are wired in series, so that one device's 'grant out' line is connected to the next device's 'grant in' line, starting the the CPU's 'grant out' line. When a device sees a 'granted' pulse on one of its grant in lines, '''if''' the device had requested a DMA/interrupt, it 'consumes' the grant pulse, and goes on to do the type of operation it requested; if it was '''not''' requesting that type of operation, it 'passes' the grant by generating a 'granted' pulse on '''its''' grant out line.
		+
		+	On systems which have [[backplane]]s into which devices can be plugged, it is usually necessary to provide some means for a grant to 'jump over' an empty backplane slot; for the UNIBUS, this is done with either a [[G727 grant continuity card\|G727]] or a [[G7273 grant continuity card\|G7273]] grant continuity card.