Abstract: This invention relates to personal computers, and more particularly to personal computers in which capability is provided for continuance of processing through an occurrence of a RESET signal while avoiding systems failures. The personal computer system has a high speed local processor data bus; an input/output data bus; a resettable microprocessor coupled directly to the local processor bus; and a bus interface controller coupled directly to the local processor bus and directly to the input/output data bus for providing communications between the local processor bus and input/output data bus. The bus interface controller provides for arbitration among devices directly coupled to the input/output data bus for access to the input/output data bus and to the local processor bus and for arbitration among the input/output data bus and the microprocessor for access to the local processor bus.

Abstract: This invention relates to personal computers, and more particularly to personal computers in which capability is provided for the usual system controlling processor to be reset, initialized and then isolated if an alternate system controller is provided for the system.

Abstract: In a personal computing system the function of the DMA controllers in the "AT" or "ISA" bus has been modified so that the system may select whether the 16-bit DMA channels are to be used as 8-bit DMA channels or 16-bit DMA channels. An 8/16-bit mode bit for each of the 16-bit DMA channels is written in a control register during the system Power On Self Test routine. Once the mode bit is written for each of the three 16-bit DMA channels, it may be read when the channel is active to select whether the channel is to operate as an 8-bit or 16-bit channel. With this mode bit information available, the page addressing may be selectively changed from 128k size pages to 64k size pages when a 16-bit DMA channel is to be converted to 8-bit. In addition, the byte addressing within a page may be changed from two byte addressing during 16-bit mode to single byte addressing during 8-bit mode.

Abstract: This invention relates to personal computer systems and, more particularly, to such a system having security features enabling control over access to data retained in such a system.

Abstract: This invention relates to personal computer systems and, more particularly, to such a system having security features enabling control over access to data retained in such a system.

Abstract: This invention relates to personal computers, and more particularly to personal computers in which arbitration for control over a data handling bus occurs among a plurality of "master" devices coupled directly to the bus and memory address signals are varied in response to such arbitration. The personal computer system has a high speed local processor data bus, an input/output data bus, a microprocessor coupled directly to the local processor bus, volatile memory coupled to the local processor bus for volatile storage of data, and a bus interface controller coupled directly to the local processor bus and directly to the input/output data bus for providing communications between the buses. The bus interface controller provides for arbitration among devices directly coupled to the input/output data bus for access to the input/output data bus and to the local processor bus, and for arbitration among the input/output data bus and said microprocessor for access to the local processor bus.

Abstract: This invention relates to personal computer systems and, more particularly, to such a system having security features enabling control over access to data retained in such a system. This invention contemplates protecting a personal computer system which has the capability of becoming a secure system from being placed into that condition by an attack on an unsecured machine. Additionally, in a network environment, it is important to maintaining network security that any given particular system be uniquely identified to the network, in order to guard against the substitution of an insecure "alternate" which would open the network to attack through an insecure system. This invention contemplates provision for such identification in a secure manner.

Abstract: A personal computer is provided with primary and secondary non-volatile storage devices for initializing the system when power is turned on. The primary device is a flash RAM. A flash ROM memory controller include means to detect when the flash ROM becomes corrupted and to switch over to the secondary device for initialization allowing the flash ROM to be later reprogrammed.

Abstract: A programmable interrupt controller having a plurality of interrupt request inquest inputs and an interrupt request output for connection to a central processing unit (CPU) includes means for interrupting the CPU over the interrupt request output responsive to an interrupt request from any one of the interrupt request inputs and a priority resolver for assigning a priority position to each of the interrupt request inputs to create an interrupt priority hierarchy. The interrupt controller is programmable such that each interrupt request input may be independently established as responsive to either edge-triggered or level-triggered interrupt requests on a per interrupt basis. An initialization command word register of the interrupt controller has a bit corresponding to each of the interrupt request inputs. Programming each of the bits of the register to one of two states determines whether corresponding interrupt request inputs are edge-sensitive or level-sensitive.

Abstract: A microcomputer system has a first, low order address, memory soldered to the planar printed circuit board and can accept further memory pluggable into a socket on the board. At power on self test, the memories are tested, and, if an error is detected in the first memory, this memory is disabled by directing the lowest order memory addresses to the second memory and reducing the highest order addresses by the number of locations in the first memory.

Abstract: In a data processing system including a main processor and a co-processor, a logic circuit is coupled to receive error and busy outputs of the co-processor to generate an interrupt output on co-incidence of active error and busy signals and to latch the busy signal to the main processor to ensure that the main processor will honor the interrupt before executing another co-processor instruction.

Abstract: A microcomputer system includes a main processor, a memory and a direct memory access controller (DMA) effective to control direct data transfer between the memory and input/output devices on channels. Bus control for data transfer is switchable between the DMA and processor by a hold request/acknowledge handshaking sequence between the DMA and processor. A control line from the channels is activated by a peripheral processing device on a channel when it wishes to gain control of the busses for data transfer. Logic means coact with the handshaking sequence to determine which device gains control of the busses. This logic is responsive to the DMA address enable output (AEN), the hold acknowledge output of the main processor (HLDA) and the channel control line output (-MASTER). When all these are deactivated, control passes to the main processor, when AEN and HLDA only are activated, control passes to the DMA controller and, when all three are activated, control passes to the peripheral processing device.

Abstract: A bi-directional serial printer has a look-ahead feature which determines the distance between the margin of the line being printed and the margin, in the direction of the print head travel, of the next line to be printed. If this distance is less than a predetermined number, print head motion continues after printing the last character on the present line until the print head reaches the margin position for the next line.