AT80SND1C-ROTIL datasheet(24/210 Pages) ATMEL

24 / 210 page

AT8xC51SND1C

4109E–8051–06/03

Figure 16. Lower 128 Bytes Internal RAM Organization

Upper 128 Bytes RAM

The upper 128 Bytes of RAM are accessible from address 80h to FFh using only indirect

addressing mode.

Expanded RAM

The on-chip 2K Bytes of expanded RAM (ERAM) are accessible from address 0000h to

07FFh using indirect addressing mode through MOVX instructions. In this address

range, EXTRAM bit in AUXR register (see Table 29) is used to select the ERAM

(default) or the XRAM. As shown in Figure 15 when EXTRAM = 0, the ERAM is selected

and when EXTRAM = 1, the XRAM is selected (see Section “External Space”).

The ERAM memory can be resized using XRS1:0 bits in AUXR register to dynamically

increase external access to the XRAM space. Table 26 details the selected ERAM size

and address range.

Table 26. ERAM Size Selection

Note:

Lower 128 Bytes RAM, Upper 128 Bytes RAM, and expanded RAM are made of volatile

memory cells. This means that the RAM content is indeterminate after power-up and

must then be initialized properly.

Bit-Addressable Space

4 Banks of

8 Registers

R0-R7

30h

7Fh

(Bit Addresses 0-7Fh)

20h

2Fh

18h

1Fh

10h

17h

08h

0Fh

00h

07h

XRS1

XRS0

ERAM Size

Address

256 Bytes

0 to 00FFh

512 Bytes

0 to 01FFh

1K Byte

0 to 03FFh

2K Bytes

0 to 07FFh

AT80SND1C-ROTIL Datenblatt(PDF) 24 Page - ATMEL Corporation

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