External bus interface pdf

Being external to the computer, external buses are much slower than internal buses. Moreover, an external bus can be both serial or parallel. By: Brad Rudisail Contributor. By: Kaushik Pal Contributor. By: Leah Zitter Contributor. Dictionary Dictionary Term of the Day.

Techopedia Terms. Connect with us. Sign up. Being external to the computer, external buses are much slower than internal buses. Moreover, an external bus can be both serial or parallel. By: Brad Rudisail Contributor. By: Kaushik Pal Contributor. By: Leah Zitter Contributor.

Dictionary Dictionary Term of the Day. Techopedia Terms. Connect with us. Sign up. The processor 54 may require a specialized debugging mode including hardware and software implementation.

In one example, the bus 58 may be implemented as a single-bit or multi-bit bus. For example, a first bit may be implemented as a test reset bit, a second bit may be implemented as a test clock bit, a third bit may be implemented as a test mode select bit, a fourth bit may be implemented as a test data input bit and a fifth bit may be implemented as a test data output bit. However, other bit widths may be implemented accordingly to meet the design criteria of a particular application.

The processor 54 may provide a non-intrusive development and debug technology that may provide high performance real-time debug features. Additionally, the system 50 may implement such debugging technology at a low system cost.

The system 50 may use a pre-existing JTAG boundary scan interface e. The system 54 may provide hardware breakpoints, unlimited software breakpoints, and real-time program counter trace with a minimum of hardware overhead. The circuit 54 may also significantly reduce system design time and cost. The processor 54 may provide specialized hardware debugging. The processor 54 may provide such specialized hardware debugging by implementing on-chip debugging circuitry.

In one example, the processor 54 may be implemented as a reduced instruction set computer RISC processor. However, other processor types may be implemented accordingly to meet the design criteria of a particular implementation. The processor 54 generally comprises an interface block or circuit , a central processor unit CPU block or circuit and an interface block or circuit The CPU may be required to provide a specialized debugging mode.

The interface circuit may be implemented as a bus interface unit BIU circuit. The circuit may be connected to the circuit through a bus Similarly, the CPU may be connected to the circuit through a bus The circuit may be connected to an external bus The bus interface unit may be implemented within a microprocessor core e.

Whenever the CPU requests an instruction fetch, the address and request are first presented to the interface via a group signal e. Next, the instruction fetch data is generally returned to the input n of the CPU through a dedicated channel e. When the CPU requests a data read, an analogous protocol is used e. The request and address are generally then presented to the interface via a group signal e.

Next, the data load is generally returned to the CPU through a dedicated channel e. When the CPU requests a data write, the address, request and data are generally presented to the interface via the group signal DATA on the bus n. The interface generally comprises a multiplexer block or circuit , a block or circuit , a block or circuit and a block or circuit In another example, the circuit may represent an external bus portion of the EJTAG interface e. In one example, the circuit e.

However, the circuits and may be implemented as other appropriate type devices in order to meet the criteria of a particular implementation. The circuit may buffer signals read from the external bus