IS89C51 datasheet(7/48 Pages) ISSI

7 / 48 page

IS89C51

Integrated Silicon Solution, Inc. — 1-800-379-4774

MC016-1C

11/21/98

ISSI®

OPERATING DESCRIPTION

The detail description of the IS89C51 included in this

description are:

• Memory Map and Registers

• Timer/Counters

• Serial Interface

• Interrupt System

• Other Information

• Flash Memory

MEMORY MAP AND REGISTERS

Memory

The IS89C51 has separate address spaces for program

and data memory. The program and data memory can be

up to 64K bytes long. The lower 4K program memory can

reside on-chip. Figure 5 shows a map of the IS89C51

program and data memory.

The IS89C51 has 128 bytes of on-chip RAM, plus numbers

of special function registers. The lower 128 bytes can be

accessed either by direct addressing or by indirect

addressing. Figure 6 shows internal data memory

organization and SFR Memory Map.

The lower 128 bytes of RAM can be divided into three

segments as listed below and shown in Figure 7.

bytes). The device after reset defaults to register bank

0. To use the other register banks, the user must select

them in software. Each register bank contains eight 1-

byte registers R0-R7. Reset initializes the stack point

to location 07H, and is incremented once to start from

08H, which is the first register of the second register

bank.

Bit Addressable Area: 16 bytes have been assigned

for this segment 20H-2FH. Each one of the 128 bits of

this segment can be directly addressed (0-7FH). Each

of the 16 bytes in this segment can also be addressed

as a byte.

Scratch Pad Area: 30H-7FH are available to the user

as data RAM. However, if the data pointer has been

initialized to this area, enough bytes should be left

aside to prevent SP data destruction.

FFFFH:

64K

0FFFH:

Program Memory

(Read Only)

Data Memory

(Read/Write)

EA = 0

External

PSEN

EA = 1

Internal

0000

FFFFH

Internal

FFH

80H

7FH

0000

RD WR

Figure 5. IS89C51 Program and Data Memory Structure

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