Three line communications method and apparatus
AssigneeHewlett-Packard Company
InventorThomas L. Antles, II
Life of this patent
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Abstract
A communications scheme is provided whereby each of a plurality of I/O devices is connected to a system controller via three lines: a bidirectional data bus, a clock bus, and a bidirectional enable/interrupt line. The enable/interrupt lines serve the dual-purpose of carrying interrupt signals from an I/O device to the system controller and carrying enable signals from the system controller to the I/O device. To avoid conflict on an enable/interrupt line, an I/O device may send an interrupt only while the clock signal is at a first level. When the clock signal is at a second level, the I/O device is required to monitor its enable/interrupt line for an enable signal from the system controller.
Claims20
A communications system for bidirectional data transfer between a master and a plurality of slaves comprising:
- a bidirectional data bus connected to the master and each slave for transferring data between the master and the slaves;
- a clock bus connected to the master and each slave for synchronizing data transfer operations;
- a plurality of bidirectional enable/interrupt lines for intermittently transmitting interrupt request signals generated by the slaves to the master on, and for transmitting enable signals generated by the master to the slaves, each enable/interrupt line connecting the master to one of the slaves, the slaves driving the enable/interrupt lines with interrupt request signals in synchrony with a clock signal on the clock bus, and first asserting the interrupt request signals asynchronously with respect to edge transitions of the clock signal.
A method of communicating between a master and a slave in a system comprising the master and a plurality of slaves, wherein each slave is connected to the master via three signal lines, the method comprising:
- holding a first of said three lines at a first signal level when not in use;
- intermittently driving the first line to a second signal level by the slave when the slave originates a data exchange in synchronization with a clock signal on the third line, to thereby interrupt the master, the slave first driving the first line to a second signal level asynchronously with respect to edge transitions of a clock signal on the third line;
- continuously driving the first line to the second signal level by the master to thereby initiate communication;
- and
- exchange data between the master and the slave on the second line in synchronization with the clock signal.
A communications system comprising a master and a plurality of slaves wherein each slave is connected to the master through first, second and third lines and the master is connected to the plurality of slaves through a number of lines equal to the number of the slaves plus two, and wherein each slave includes means for intermittently applying an interrupt signal to the first line in synchrony with a clock signal on the second line, said means first applying the interrupt signal to the first line asynchronously with respect to edge transitions of the clock signal.
A communications/control method for a system comprised of a method device and a plurality of slave devices, wherein the method includes connecting each slave device to the master device by a single wire, and transferring both enable signals from the master to a slave and interrupt request signals from the slave to the master, over said same single wire wherein transferring interrupt request signals includes initially asserting the interrupt request signals asynchronously with respect to edge transitions of a clock signal applied to all of the slave devices, and in which the interrupt request signals change levels in synchrony with a clock signal applied to all of the slave devices.
Dependencies are inferred from the claim text.