TSC80251G2D(2006) Ver la hoja de datos (PDF) - Atmel Corporation

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TSC80251G2D
(Rev.:2006)

8/16-bit Microcontroller with Serial Communication Interfaces

Atmel Corporation 

AT/TSC8x251G2D

Address Spaces

Program/Code Memory

The TSC80251G2D derivatives implement four different address spaces:

• On-chip ROM program/code memory (not present in ROMless devices)

• On-chip RAM data memory

• Special Function Registers (SFRs)

• Configuration array

The TSC83251G2D and TSC87251G2D implement 32 KB of on-chip program/code

memory. Figure 4 shows the split of the internal and external program/code memory

spaces. If EA# is tied to a high level, the 32-Kbyte on-chip program memory is mapped

in the lower part of segment FF: where the C251 core jumps after reset. The rest of the

program/code memory space is mapped to the external memory. If EA# is tied to a low

level, the internal program/code memory is not used and all the accesses are directed to

the external memory.

The TSC83251G2D products provide the internal program/code memory in a masked

ROM memory while the TSC87251G2D products provide it in an EPROM memory. For

the TSC80251G2D products, there is no internal program/code memory and EA# must

be tied to a low level.

Figure 4. Program/Code Memory Mapping

Program/code

Program/code

External Memory Space

Segments

32 KB

32 KB

EA# = 0

FF:FFFFh

FF:8000h

FF:7FFFh

FF:0000h

FE:FFFFh

EA# = 1

On-chip ROM/EPROM

Code Memory

32 KB

64 KB

FE:0000h

FD:FFFFh

Reserved

02:0000h

01:FFFFh

128 KB

01:0000h

00:FFFFh

4135F–8051–11/06

00:0000h

Note:

Special care should be taken when the Program Counter (PC) increments:

If the program executes exclusively from on-chip code memory (not from external mem-

ory), beware of executing code from the upper eight bytes of the on-chip ROM

(FF:7FF8h-FF:7FFFh). Because of its pipeline capability, the TSC80251G2D derivative

may attempt to prefetch code from external memory (at an address above FF:7FFFh)

and thereby disrupt I/O Ports 0 and 2. Fetching code constants from these 8 bytes does

not affect Ports 0 and 2.

When PC reaches the end of segment FF:, it loops to the reset address FF:0000h (for

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