7721 datasheet(32/577 Pages) RENESAS

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Giải thích chi tiết về linh kiện	16-BIT SINGLE-CHIP MICROCOMPUTER

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CENTRAL PROCESSING UNIT (CPU)

7721 Group User’s Manual

2–9

2.2 Bus interface unit

A bus interface unit (BIU) is built-in between the central processing unit (CPU) and memory•I/O devices.

BIU’s function and operation are described below.

When externally connecting devices, refer to “CHAPTER 3. CONNECTION WITH EXTERNAL DEVICES.”

2.2.1 Overview

Transfer operation between the CPU and memory•I/O devices is always performed via the BIU.

The BIU reads an instruction from the memory before the CPU executes it.

When the CPU reads data from the memory•I/O device, the CPU first specifies the address from which

data is read to the BIU. The BIU reads data from the specified address and passes it to the CPU.

When the CPU writes data to the memory•I/O device, the CPU first specifies the address to which data

is written to the BIU and write data. The BIU writes the data to the specified address.

To perform the above operations to , the BIU inputs and outputs the control signals, and control the

bus.

Figure 2.2.1 shows the bus and bus interface unit (BIU).

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