Datasheet

36
A/T89C51CC01
4129N–CAN–03/08
FM0 Memory Architecture The Flash memory is made up of 4 blocks (see Figure 20):
• The memory array (user space) 32K Bytes
• The Extra Row
• The Hardware security bits
• The column latch registers
User Space This space is composed of a 32K Bytes Flash memory organized in 256 pages of 128
Bytes. It contains the user’s application code.
Extra Row (XRow) This row is a part of FM0 and has a size of 128 Bytes. The extra row may contain infor-
mation for boot loader usage.
Hardware Security Byte The Hardware security Byte space is a part of FM0 and has a size of 1 byte.
The 4 MSB can be read/written by software, the 4 LSB can only be read by software and
written by hardware in parallel mode.
Column Latches The column latches, also part of FM0, have a size of full page (128 Bytes).
The column latches are the entrance buffers of the three previous memory locations
(user array, XROW and Hardware security byte).
Cross Flash Memory Access
Description
The FM0 memory can be program only from FM1. Programming FM0 from FM0 or from
external memory is impossible.
The FM1 memory can be program only by parallel programming.
The Table 24 show all software Flash access allowed.
Table 24. Cross Flash Memory Access
Code executing from
Action
FM0
(user Flash)
FM1
(boot Flash)
FM0
(user Flash)
Read ok -
Load column latch ok -
Write - -
FM1
(boot Flash)
Read ok ok
Load column latch ok -
Write ok -
External
memory
EA = 0
Read - -
Load column latch - -
Write - -