Philips Electronics North America Corporation

North American Philips Corp, Signetics Division

Gregory K Goodhue

Farrell Lynn Ostler

Ori K Mizrahi-Shalom

Neil Edward Birns

William J Price

Santanu Roy

Ronald L Treadway

Ata R Khan

Kevin A Sholander

Brian M Willis

A microcontroller with selectable function external pins. Program controllable configuration registers control pin function selection through multiplexers which select between data/address lines and special function unit output lines and which control line drivers which are disabled when the pins are used as input pins.

Pin selection system for microcontroller having multiplexer selects

In a computer system, especially a microcontroller, a circuit for protecting hardware-modifiable status bits during a read-modify-write operation, which circuit is relatively simple to implement yet operates well and does not require an undue amount of die real estate to implement. The circuit comprises means for storing information representing whether a hardware-modifiable status bit has been updated during a read-modify-write operation, and means to prevent over-writing of the status bit during the write portion of the read-modify-write cycle when the stored information is detected. The means for storing the information comprises a latch set into its first state whose output indicates whether the first state exists. That output is connected to logic circuitry which blocks the rewrite portion of the read-modify-write operation from changing a hardware-modified bit set during that cycle.

System for write protecting a bit that is hardware modified during a

An instruction prefetch system for a digital processor, and in particular a microcontroller which includes the prefetch system and instruction queue normally provided as part of the instruction fetch unit, to which is added a second instruction prefetch buffer in the system, preferably in the bus interface unit which serves as the memory interface unit. This added prefetch buffer has storage for only a small number of bytes or words, and operates to supply prefetched instructions to the queue in the instruction fetch unit. However, it operates under the following constraint: it only prefetches within the boundaries of each small block of code memory and stalls when a block boundary is reached until a new address appears. This approach combines some cache and prefetch principles for a limited cost design.

Computer instruction prefetch system

A microcontroller which directly drives a memory with low order address bits during a fetch operation. Driving the low order address bits directly while the high order bits are latched during an address/data multiplex on the same pins allows the latch enable cycle to be skipped during sequential fetches. A sequential address detector indicates when the latch enable cycle can be skipped.

High speed memory access system for a microcontroller with directly

Page-mode-organized ROMs and associated circuitry are connected only to data and control buses in an information processing system. Addressing and reading of the ROMs are controlled by a processor without connecting the ROMs to an address bus. Selection of a particular ROM and of a particular page in the selected ROM is accomplished by applying a first control signal to the control bus and a first data word to the data bus. This first data word thus serves as the address of the selected page in the selected ROM. Then a particular byte of the selected page is selected by applying a second control signal to the control bus and a second data word to the data bus. This second data word serves as the address of the selected byte. Subsequently, in response to a third control signal, the selected byte is read out of the selected ROM and applied to the data bus.

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San Jose, CA, United States of America

Gregory K Goodhue