TSC87251G1A-16CA 参数 Datasheet PDF下载

TSC87251G1A

6. Address Spaces

The TSC87251G1A implements four different address spaces:

D

On–chip EPROM/OTPROM program/code memory

D

On–chip RAM data memory

D

Special Function Registers (SFRs)

D

Configuration array

6.1. Program/Code Memory

The TSC87251G1A implements 16 Kbytes of on–chip EPROM/OTPROM for 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 16–Kbyte on–chip

program/code 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.

Program/code

External Memory Space

48 Kbytes

16 Kbytes

FF:4000h

FF:3FFFh

EA#= 0

EA#= 1

FF:0000h

FE:FFFFh

16 Kbytes

Program/code

Segments

FF:FFFFh

On–chip Memory

EPROM/OTPROM Code

64 Kbytes

128 Kbytes

Figure 4. Program/Code Memory Mapping

Notes:

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

– If the program executes exclusively from on–chip code memory (not from external memory), beware of executing code from the upper eight bytes of

the on–chip EPROM (FF:3FF8h–FF:3FFFFh). Because of its pipeline capability, the TSC87251G1A may attempt to prefetch code from external

memory (at an address above FF:3FFFFh) 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 compatibility with the C51 Architecture). When PC increments

beyond the end of segment FE:, it continues at the reset address FF:0000h (linearity). When PC increments beyond the end of segment 01:, it loops to

the beginning of segment 00: (this prevents from its going into the reserved area).

8

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01:0000h

00:FFFFh

00:0000h

Rev. A

–

September 21, 1998

FE:0000h

FD:FFFFh

Reserved

02:0000h

01:FFFFh