User Manual

T89C51AC2

Rev. B – 19-Dec-01

7. Data Memory The T89C51AC2 p rovides data memory access in two d ifferent spaces:

1. The internal spac e mapped in three separate segments:

• the lower 128 bytes R AM segment.

• the upper 128 bytes R AM segment.

• the ex panded 1024 bytes RAM segment (ERAM ).

2. The external space.

A f ourth in ternal seg ment is avail able but ded icated t o Speci al Func tion R egisters,

SF Rs, (addresses 80h to

FFh) access ible by direc t addressing mode.

Figure 2 shows t he internal and extern al data memory spaces organization.

Figure 1. Internal memory - RAM

Figure 2. Internal and External Data M emory O rganizat ion ERAM-XRAM

Upper

128 bytes

Internal RAM

Lower

128 bytes

Internal RAM

Special

Function

Registers

80h

00h

FFh

direct addressing

addressing

7Fh

direct or indirect

indirect addressing

256upto1024bytes

00h

64 Kbytes

External XRAM

0000h

FFFFh

Internal ERAM

EXTRAM= 0

EXTRAM= 1

FFh or 3FFh

Internal

External