Abstract: A memory expansion scheme is provided which permits a program to automatically cross memory bank boundaries, without user intervention. A memory bank address register stores a value corresponding to a selected memory bank (i.e. Bank 0), in a 4-bit subfield (K-Field). In the preferred embodiment, the K-Field is implemented using six (6) bank number registers, each of which is coupled to the corresponding address register, to form a 20-bit (extended) logical address. During an effective address calculation, in the index addressing mode, a 16-bit logical offset address, stored in an offset register, is added to the 20-bit (extended) logical address, by an adder in the ALU. The adder transfers a 20-bit physical address onto an address bus, via an address buffer. When the calculated address crosses a memory bank boundary, the upper four (4) address bits (A.sub.16 -A.sub.19) are automatically updated, thereby enabling the program to cross a memory bank boundary without user intervention.

Abstract: In a data processor an Sweeney-Robertson-Tocher (SRT) divider is provided having a negative divisor sticky detection circuit. The negative divisor sticky detection circuit allows negative sticky correction to occur in the SRT divider without requiring additional iteration cycles. At the conclusion of iterative cycles of a divide operation, a final remainder is formed and stored in a latch in the SRT divider. The negative divisor sticky detection circuit determines whether a negative final remainder is equal in magnitude to a divisor value by bit-wise XORing the final remainder with the two's complement value of a divisor, immediately before sticky logic detects the negative sticky bit. The final sticky value is obtained by logically combining the negative sticky bit with a positive sticky bit computed by a positive divisor sticky detection circuit.

Abstract: A microcontroller is provided having an on-chip electrically erasable programmable read-only-memory (EEPROM), which is user programmable via a programming register. The microcontroller includes a low voltage program inhibit (LVPI) circuit which is combined with the existing EEPROM design. By integrating the LVPI circuit into the EEPROM, the EEPROM may be protected without disabling the entire data processing system. If the supply voltage (V.sub.DD) falls below a predetermined voltage level, the LVPI circuit inhibits the use of the EEPROM programming register, thereby preventing the CPU from programming or erasing the EEPROM. A comparator in the LVPI circuit compares a precision reference voltage to a voltage divided off of the power supply (V.sub.DD), and provides a output signal to the EEPROM programming register. During normal operation, the comparator output signal is a logic low, which enables the user to program or erase the EEPROM, via the programming register.

Abstract: A data processor is provided for reloading deferred pushes in copy-back cache. When a cache "miss" occurs, a cache controller selects a cache line for replacement, and request a burst line read to transfer the required cache line from an external memory. When the date entries in the cache line selected for replacement are marked dirty, the cache controller "pushes" the cache line or dirty portions thereof into a buffer, which stores the cache line pending completion, by a bus interface controller, or the burst line read. When the burst line read terminates abnormally, due to a bus error or bus cache inhibit (or any other reason), the data cache controller reloads the copy-back cache with the cache line stored in the buffer. The reloading of the copy-back cache avoids the potential for multiple concurrent exception conditions, and eliminates the problem of unnecessarily removing an otherwise valid cache entry from the cache.

Abstract: A block MOVE instruction allows a programmer to issue an instruction to a loosely coupled system bus controller, thereby facilitating the execution of a memory to memory move of multiple data entries, utilizing a burst mode transfer onto the system bus for both reads and writes. The instruction allows the programmer to fully utilize the maximum bus bandwidth of the system bus for memory to memory transfers of data (e.g. DMA, block moves, memory page initialization) and transfers of instructions/data to detached coprocessors.

Abstract: A digital phase lock loop that does not depend on a voltage controlled oscillator (VCO) for phase locking. A phase detector (PD), terminated with a latch, controls an up/down counter that programs an increase/decrease of delay on the delay line. The tapped output of the delay line goes through a two phase generator which in turn feeds back to the PD for comparison with the reference clock. This process is repeated until phase locking is obtained.

Abstract: A data processing system is provided having a secondary cache for performing a deferred cache load. The data processing system has a pipelined integer unit which uses an instruction prefetch unit (IPU) to maintain a steady stream of instructions to the pipeline. The (IPU) issues prefetch requests to a cache controller on a cache half-line basis. In conjunction with the prefetch request, the IPU transfers a prefetch address to a cache address memory management unit (CAMMU), for translation into a corresponding physical address. The physical address is compared with the indexed entries in a primary cache, and compared with the physical address corresponding to the single cache line stored in the secondary cache. When a prefetch miss occurs in both the primary and the secondary cache, the cache controller issues a bus transfer request to retrieve the requested cache line from an external memory.

Abstract: A data cache capable of operation in a write-back (copyback) mode. The data cache design provides a mechanism for making the data cache coherent with memory, without writing the entire cache entry to memory, thereby reducing bus utilization. Each data cache entry is comprised of three items: data, a tag address, and a mixed size status field. The mixed size status fields provide one bit to indicate the validity of the data cache entry and multiple bits to indicate if the entry contains data that has not been written to memory (dirtiness). Multiple dirty bits provide a data cache controller with sufficient information to minimize the number of memory accesses used to unload a dirty entry. The data cache controller uses the multiple dirty bits to determine the quantity and type of accesses required to write the dirty data to memory. The portions of the entry being replaced that are clean (unmodified) are not written to memory.

Abstract: A replacement method is provided for improving the hit rate and testability of a page address translation cache (PATC). The replacement scheme uses a modified FIFO replacement algorithm. A circular shift register has a pointer which points to each of a predetermined number of translation descriptors stored in the PATC. The shift register pointer has an input for receiving the logic state of a valid bit associated with each of the translation descriptors stored in the PATC. The shift register is advanced after every translation cycle, until the logic state of the valid bit indicates that the denoted translation descriptor is invalid, or until a read/write control signal indicates a PATC write is in progress. Upon detecting an invalid translation descriptor, the circular shift register is disabled, and remains disabled until an address translation "miss" occurs, and a replacement entry is loaded into the PATC. If, however, an address translation miss occurs while the circular shift register is enabled (i.e.

Abstract: A data processor having a split level control store structure, which partitions program memory into a macrocode portion and a microcode portion. The data processor contains two distinct machines, a macromachine and a micromachine. The macromachine includes an instruction sequence controller which detects the macrocode branch instruction before it is perceived by the micromachine, extracts from the branch instruction a macroaddress, and then provides the extracted macroaddress to the program memory as the next sequential instruction address. By "pipelining" the macromachine, the macromachine can "execute" the branch instruction in parallel with, and independent of, the execution by the micromachine of the preceeding instruction.

Abstract: A data processing system having a debug peripheral is provided. The debug peripheral is coupled to a central processing unit and memory via an internal communications bus. The debug peripheral is a single-word dual port memory with parallel read-write write access on one side, and synchronous, full-duplex serial read-write access on the other side. The serial side of the debug peripheral is connected to external emulation hardware by means of a three-pin synchronous serial interface. The parallel access is via a connection to a core central processing unit (CPU) internal communications bus. The debug peripheral is addressed at sixteen adjacent locations in the CPU memory space. During a debug interlude, the debug peripheral assumes control of the CPU by providing an interrup signal to the CPU, and thereby causing the CPU to fetch instructions directly from the debug peripheral.

Abstract: A design for a structured scan path circuit incorporating domino logic circuitry is provided. The scan path circuit allows the rapid evaluation of a predetermined logic function, while allowing the use of automatic test pattern generation programs. Each function input signal has its own latch, the equivalent to the master latch in a standard scan flip-flop. The domino function output also has a latch, the equivalent of the slave latch in the scan flip-flop. The use of the input latches eliminates the need to insure the stability of the function input signals during the evaluation of the domino logic function. Thus, the input latches eliminate the potential "hazard" problems which can occur due to the instability of the input signals during evaluation of the domino logic function. A scan enable signal selectively enables and disables the function evaluation by the domino logic circuitry.

Abstract: A toggle-free scan flip-flop (TFSFF) is provided which is designed for use during a test mode scan operation. The toggle-free scan flip-flop has the capability of not toggling its parallel output during test mode scan operation. The TFSFF uses a master latch, which is controlled by a scan multiplexor, to selectively update two alternate slave latches. Switching logic controls the determination of which alternate slave latch is updated with the incoming data signal. An existent scan enable (SE) signal controls the switching logic, and thus, the TFSFF design requires no additional control signals for its operation. During the scan test mode, the data is clocked through the TFSFF from a Scan-Data-In terminal, and out the Scan-Data-Out terminal, without affecting the system data output Q. The shift sequence is followed by a capture interval, during which the Q output is automatically updated with the desired data to test the target logic.

Abstract: A single-ended sense amplifier, for fast sensing from a precharged low condition, is provided. In the precharge mode, the amplifier discharges the sensing node to ground, and charges a bias node to a first predetermined voltage. This bias node modulates the current drive capabilities of the first and second charge transistors. Once the sense amplifier enters the sensing mode, the voltage at the bias node causes the first charge transistor to rapidly supply a substantial amount of current to the sensing node. If the selected memory cell is in the conducting state, the voltage at the sense node is discharged to ground and the amplifier output is a low-voltage, indicating the detection of a logic "0" state. Conversely, if the selected memory cell is in a non-conducting state, the voltage at the sense node increases beyond a second predetermined voltage, and the amplifier output is a high-voltage, indicating the detection of a logic "1".

Abstract: An EPROM memory transistor programming arrangement is disclosed in which programming voltage for a memory transistor is applied via a load line of series connected N-channel MOS transistors which are controlled by low voltage NAND gate having low voltage address, write select and data inputs, through a high voltage inverter. The arrangement may be implemented entirely by N-channel MOS transistors which enables a compact silicon implementation and requires no separate BVDSS breakdown protection.

Abstract: An output buffer with reduced supply line disturbance is provided for use in high performance microprocessor circuits. The output buffer uses a resistor and transistor as a sensing circuit, in parallel with an output driver transistor, thereby providing a negative feedback path into the control circuitry for the output driver. The sensing circuit detects the strength of the output driver transistor, by monitoring the amount of capacitance on the output node when the output buffer is driving the output signal to a logic high or logic low state, and rapidly produces a control voltage. The current flowing through the driver transistor and the sensor transistor causes a voltage drop across the resistor, which is fedback into the control circuitry. The control voltage is fed back into the output buffer control circuitry, thereby facilitating the reduction of the current drive capabilities of the driver and sensor transistors.