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M6759

8-bit MTP Micro-controller

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--Proprietary, Confidential, Preliminary--

Acer Laboratories Inc.

M6759: 8 bit MTP Micro-controller

Section 3 : Function Description

3.1 Data Space Addressing

The M6759 has internal data memory that is mapped into

four separate segments: the lower 128 bytes of RAM,

upper 128 bytes of RAM, 128 bytes Special Function

Register (SFR), and 256 bytes auxiliary RAM (ARAM).

The four segments are:

1. The Lower 128 bytes of RAM (address 00H to 7FH) are

directly and indirectly addressable.

2. The Upper 128 bytes of RAM (address 80H to FFH) are

indirectly addressable only.

3. The Special Function Registers SFRs, (address 80H to

FFH) are directly addressable only.

4. The 256-bytes auxiliary RAM (ARAM, 0000H-00FFH)

are indirectly accessed by move external instruction,

MOVX.

Either direct or indirect addressing can access the lower

128 bytes. The upper 128 bytes can be accessed by

indirect address only. The upper 128 bytes occupy the

same address space as the SFRs. That means they have

the same address, but are physically separate from SFR

space.

The ARAM can be accessed by indirect addressing and

MOVX instructions when ARAM_EN bit is set. This part of

memory is physically located on-chip, logically occupied

the first 256-bytes of external data memory if ARAM_EN

bit is set.

The ARAM is indirectly addressed, using the MOVX

instruction in combination with any of the registers R0, R1

of the selected bank or DPTR. An access to ARAM will not

affect ports P0, P3.6 (/WR) and P3.7 (/RD).

If ARAM_EN is cleared, the access to external memory

will be performed in the same way as standard 8051.

If ARAM_EN is set and DPTR contains value lower than

0100H, the ARAM will be accessed rather than external

memory, but if DPTR contains value higher than 00FFH

(i.e. 0100H to FFFFH), the external memory will be

accessed.

If ARAM_EN is set and P2 SFR contains 00H, the ARAM

will be accessed by the MOVX @Ri, #data instruction, but

if P2 SFR contains a non-zero value, the external memory

will be accessed using MOVX @Ri, #data.

For example,

MOVX

DPTR, #data

If ARAM_EN is set and DPTR contains 0030H, access the

ARAM at address 030H rather than external memory.

If ARAM_EN is set and DPTR contains 0130H, the

external memory address 0130H will be accessed

For example:

MOVX

@R0, #data

If ARAM_EN is set, P2 SFR contains 00H, and R0

contains 30H, an access to the ARAM at address 30H will

be performed.

If ARAM_EN is set, P2 SFR contains 01H, and R0

contains 30H, an access to the external memory address

0130H will be performed if P2 is connected to the high

byte address bus of external RAM.

3.2 Dual Data Pointer

Data memory block moves can be accelerated using the

Dual Data Pointer (DPTR). The standard 8051 DPTR is a

16-bit value that is used to address off-chip data RAM or

peripherals. In the M6759, the standard 16-bit data

pointer is called DPTR0 and is located at SFR address

82H and 83H. These are the standard locations. The new

DPTR is located at SFR 84H and 85H and is called

DPTR1. The new DPTR Select bit (DPS) chooses the

active pointer and is located at the LSB of the SFR

location 86H. No other bits in register 86H have any effect

and are set to 0. The user switches between data pointer

by toggling the LSB of register 86H. The increment (INC)

instruction is the fastest way to accomplish this. All

DPTR-related instructions use the currently selected

DPTR for any activity.

3.3 Low EMI Mode

In normal operation ALE is emitted at a constant rate of

1/6 the oscillator frequency, and may be used for external

timing or clocking purpose. Note, however, that one ALE

pulse is skipped during each access to external Data

Memory.

If desired, setting bit 0 of SFR location 8EH can disable

ALE operation. With the bit set, ALE is active only during

a MOVX instruction. Otherwise the pin is weakly pulled

high. Setting the ALE-disable bit has no effect if the

micro-controller is in external execution mode.

Page 6

Ver.1.01, Doc. No.: 6759DS02.doc

Acer Labs: 11F, no.45 Tung Hsing Road, Taipei 110, Taiwan, R.O.C. Tel: 886-2-8768-2800 Fax: 886-2-8768-3030

Homepage: www.ali.com.tw

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