Electrical computers and digital data processing systems: input/ – Intrasystem connection – Bus access regulation
Reexamination Certificate
1994-01-24
2001-09-25
Shin, Christopher B. (Department: 2782)
Electrical computers and digital data processing systems: input/
Intrasystem connection
Bus access regulation
C710S100000, C710S106000, C710S120000
Reexamination Certificate
active
06295572
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the SCSI (Small Computer Systems Interface) and Ethernet adapter boards used in personal computers which interface with the PCI (Peripheral Component Interconnect) Local Bus. More particularly, the present invention relates to replacement of the SCSI and Ethernet adapter boards with a single chip.
2. Description of the Prior Art
The PCI Local Bus is a high performance, 32-bit or 64-bit bus with multiplexed address and data lines. As illustrated in
FIG. 1
, the PCI Local Bus
100
is intended for use as an interconnect mechanism between peripheral controller components, such as the SCSI adapter board
102
, Ethernet adapter board
104
, and processor/memory system
106
. A PCI Local Bus Specification, Rev. 2.0, effective Apr. 30, 1993 includes protocol, electrical, mechanical and configuration requirements for the PCI Local Bus components and expansion boards. Further information concerning the PCI Local Bus specification can be obtained from the PCI Special Interest Group, M/S HF3-15A, 5200 NE Elam Young Parkway, Hillsboro, Oreg. 97124-6497.
Ethernet is a standard in personal computer networking. An Ethernet adapter board provides components for transmitting and receiving signals on a network allowing a personal computer in which it resides to be networked with other personal computers. A PCI bus interface unit on the Ethernet adapter board interfaces the adapter board with the PCI Local Bus on which a CPU resides. The PCI bus interface unit may provide digital signals to control the PCI Local Bus.
SCSI is a standard that allows users to easily add up to seven peripheral devices on a personal computer such as CD-ROM and high capacity disk drives. A SCSI adapter board in a personal computer provides digital address, data, and control signals to a SCSI bus on which peripheral devices reside. A PCI bus interface unit on the SCSI adapter board interfaces the adapter board with the PCI Local Bus on which a CPU resides. The PCI bus interface unit may provide digital signals to control the PCI bus.
Previously, manufacturers have provided Ethernet and SCSI components spaced apart on separate adapter boards. The high current requirements for digital signals transmitted and received on the PCI and SCSI buses means that the digital signals can generate significant noise. With sensitive analog components in the Ethernet controller, such as the phase lock loop (PLL) circuitry, such noise has prohibited integration of components of the Ethernet and SCSI adapter boards.
SUMMARY OF THE INVENTION
The present invention enables integration of the SCSI and Ethernet adapter board components by reducing noise generated by the digital signals resulting in very stable analog circuitry.
The present invention is an integration of components of SCSI and Ethernet adapter boards onto a single chip forming an integrated SCSI-Ethernet controller for use on a PCI Local Bus.
The present invention first reduces noise by reducing ground bounce on V
SS
pins connected to digital output buffers of the integrated SCSI-Ethernet controller. Ground bounce on V
SS
pins is first reduced by providing substantially more V
SS
pins than VDD pins to support large output buffers which continually switch current, each V
SS
pin supporting a limited number of buffers in a local area near the pin. The reduced current which each V
SS
pin has to sink, as well as limited line lengths to the V
SS
pin reduces inductance resulting in reduced ground bounce. To further reduce ground bounce, separate lines are provided from each output buffer to a V
SS
pin. By using separate lines, ground bounce resulting when multiple buffers switch together is reduced.
The present invention further reduces noise by utilizing circuitry for digital output buffers which limits the change in current over time (di/dt) during a signal transition. By limiting di/dt, noise created in the analog circuitry due to inductance is likewise limited.
The present invention additionally reduces noise by topologically organizing the digital control circuitry so that current density increases in a direction away from the analog circuitry.
Finally, the present invention reduces noise by preventing unnecessary current flow between separate analog and digital power supplies which may transfer noise between digital and analog components. Such current flow between the analog and digital power supplies is prevented by utilizing silicon control rectifiers (SCRs). SCRs are placed between power supplies. The SCRs enable current flow between the digital and analog supplies to prevent latch up should only one supply be turned on.
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IC Puts Ethernet and SCSI on a Motherboard , by John Novellino (article from Electronic Design, Jan. 24, 1994), pp. 59-60, 62 and 66.
Der Neue Champion, PCI ist da: die ersten Boards und Karten im Test, by Georg Schnurer (article in Bussysteme Report, c't 1993, Hett 10), pp. 120-122.
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