Electrical computers and digital data processing systems: input/ – Intrasystem connection – Bus access regulation
Patent
1998-09-29
2000-07-11
Ray, Gopal C.
Electrical computers and digital data processing systems: input/
Intrasystem connection
Bus access regulation
710100, 326 56, G06F 1300, G06F 1340, H03K 190175
Patent
active
060887567
ABSTRACT:
A driver circuit includes both a conventional three state mode of operation and a five state operating mode. In the three state mode of operation, the output of the driver can be in logical 0 or logical 1 "voltage source" states, as well as a very high impedance state. In addition to these three states, the output of the driver in the five state mode of operation can also be in logical 1 and logical 0 "current source" states. The voltage source states are characterized by low output impedance (e.g., 30 Ohms), while the current source states are characterized by higher output impedance (e.g., 600 Ohms). The driver circuit is particularly useful for eliminating turnaround cycles on a multiplexed address/data bus. When coupled to such a bus, the clock line is used to select the voltage source mode during the first half of the clock cycle, and the current source mode during the last half of the clock cycle. Thus, two drivers that are coupled to the same line of the bus are prevented from being switched ON in the voltage source mode at the same time, which could otherwise occur momentarily during the transition from one clock cycle to the next.
REFERENCES:
patent: 4082964 (1978-04-01), Gies
patent: 4771428 (1988-09-01), Acuff et al.
patent: 5381059 (1995-01-01), Douglas
patent: 5804985 (1998-09-01), Shieh et al.
patent: 5941997 (1999-08-01), Greaves
International Business Machines - Corporation
McKinley Martin J.
Ray Gopal C.
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