Abstract: An embedded microprocessor control system temporarily slows a microprocessor clock input signal in response to a reset strobe. This permits the peripherals to synchronize the classification of their clock phases with 386 microprocessor clock phase classifications.

Abstract: When a load instruction is encountered, a read operation is sent to the bus control logic, the register is marked as busy, and execution proceeds to the next instruction. When an instruction is executed, it proceeds providing that its source and destination registers are not marked busy; otherwise the instruction is retried. When data are returned as the result of a read operation, the destination register(s) are marked as not busy.

Abstract: Apparatus for performing mixed precision calculations in the floating point unit of a microprocessor from a single instruction opcode. 80-bit floating-point registers (44) may be specified as the source or destination address of a floating-point instruction. When the address range of the destination indicates (26) that a floating point register is addressed, the result of that operation is not rounded to the precision specified by the instruction, but is rounded (58) to extended 80-bit precision and loaded into the floating point register (FP-44). When the address range of the source indicates (26) that an FP register is addressed, the data is loaded from the FP register in extended precision, regardless of the precision specified by the instruction. In this way, real and long-real operations can be made to use extended precision numbers without explicitly specifying that in the opcode.

Abstract: An external timing source (40) provides an input waveform (44, 46) of signal voltage transitions which occur at a first frequency, which is twice the frequency desired by the internal clock. A divider circuit (48) divides the input waveform (44, 46) into a pair of intermediate waveforms (60, 62). The intermediate waveforms have signal-voltage transitions of opposing polarity which occur at a second frequency that is one-half of the first frequency. The input waveforms and the intermediate waveforms are supplied to a driver circuit (64). The driver circuit utilizes the intermediate waveforms occurring at the divided-down frequency and the input waveform occurring at the system clock frequency to produce a pair of final waveforms (66, 68). The final waveforms have signal voltage transistions of opposing polarity occurring at the divided-down frequency, but triggerred by and in synchronism with the input waveform occurring at the external clock frequency.

Abstract: A plurality of global registers are provided on the microprocessor chip. One of a global registers is a frame pointer register containing the current frame pointer, and the remainder of the global registers are available to a current process as general registers. A plurality of floating point registers are also provided for use by the current process in execution of floating point arithmetic operations. A register set pool made up of a plurality of register sets is provided, each register set being comprised of a number of local registers. When a call instruction is decoded, a register set of local registers from the register set pool is allocated to the called procedure, and the frame pointer register is initialized. When a return instruction is decoded, the register set is freed for allocation to another procedure called by a subsequent call instruction.

Abstract: A content addressable memory including a pair of column lines (54, 56) upon which information to be matched with the contents of said memory is placed. The memory is driven by a clock such that during particular clock phase a ROW line (50) and a MATCH line (52) are precharged and both column lines are discharged. The memory cell is comprised of transistors (M1, M2, M3, M4) connected to each other and to a supply voltage (Vcc) to thereby form a cross-coupled inverter storage device. Transistors (M5, M6) are connected to diode transistor (M7) and between the cross-coupled inverter (M1, M2, M3, M4) and column lines (54, 56) to thereby form and XOR gate on said column lines (54, 56) and diode transistor (M7). The diode transistor is connected between transistors (M5, M6), ROW line (50) and MATCH line (52), such that during CAM matches the diode transistor allows charge to be siphoned from MATCH line ( 52) and during a write to said CAM cell allows charge to build up.