T89C51AC2-RLSI-M datasheet(18/117 Pages) ATMEL

18 / 117 page

Draft.A - March 30, 2001

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T89C51AC2

7. Program/Code Memory

7.1. Introduction

The T89C51AC2 implement 32 Kbytes of on-chip program/code memory. Figure 8 shows the split of internal and

external program/code memory spaces depending on the product.

The FLASH memory increases EPROM and ROM functionality by in-circuit electrical erasure and programming.

Thanks to the internal charge pump, the high voltage needed for programming or erasing FLASH cells is generated

on-chip using the standard VDD voltage. Thus, the FLASH Memory can be programmed using only one voltage

and allows in application software programming commonly known as IAP. Hardware programming mode is also

available using specific programming tool.

Figure 8. Program/Code Memory Organization

Caution:

1. If the program executes exclusively from on-chip code memory (not from external memory), beware of executing code from the upper byte

of on-chip memory (7FFFh) and thereby disrupt I/O Ports 0 and 2 due to external prefetch. Fetching code constant from this location

does not affect Ports 0 and 2.

7.2. External Code Memory Access

7.2.1. Memory Interface

The external memory interface comprises the external bus (port 0 and port 2) as well as the bus control signals

(PSEN#, and ALE).

Figure 9 shows the structure of the external address bus. P0 carries address A7:0 while P2 carries address A15:8.

Data D7:0 is multiplexed with A7:0 on P0. Table 12 describes the external memory interface signals.

0000h

32 Kbytes

7FFFh1

FLASH

32 Kbytes

External Code

FFFFh

T89C51AC2

8000h

T89C51AC2-RLSI-M 数据表(PDF) 18 Page - ATMEL Corporation