Boot Mode; Functions To Prevent Flash Memory From Rewriting - Renesas M16C/60 Series Hardware Manual

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M16C/6N5 Group

Boot Mode

After a hardware reset which is performed by applying a low-level signal to the P5
signal to the CNV and P5
SS
the boot ROM area.
During boot mode, the boot ROM and user ROM areas are switched over by the FMR05 bit in the FMR0 register.
The boot ROM area contains a standard serial I/O mode and CAN I/O mode based rewrite control program
which was stored in it when shipped from the factory.
The boot ROM area can be rewritten in parallel input/output mode. Prepare an EW0 mode based rewrite
control program and write it in the boot ROM area, and the flash memory can be rewritten as suitable for the
system.

Functions to Prevent Flash Memory from Rewriting

To prevent the flash memory from being read or rewritten easily, parallel I/O mode has a ROM code protect
and standard serial I/O mode and CAN I/O mode have an ID code check function.
• ROM Code Protect Function
The ROM code protect function inhibits the flash memory from being read or rewritten during parallel I/O
mode. Figure 1.22.2 shows the ROMCP register.
The ROMCP register is located in the user ROM area. The ROMCP1 bit consists of two bits. The ROM
code protect function is enabled by setting one or both of two ROMCP1 bits to "0" when the ROMCR bits
are not "00 ", with the flash memory thereby protected against reading or rewriting. Conversely, when the
2
ROMCR bits are "00
ROM code protect function is enabled, the ROMCR bits cannot be changed during parallel I/O mode.
Therefore, use standard serial I/O mode or other modes to rewrite the flash memory.
• ID Code Check Function
Use this function in standard serial I/O mode and CAN I/O mode. Unless the flash memory is blank, the ID
codes sent from the programmer and the ID codes written in the flash memory are compared to see if
they match. If the ID codes do not match, the commands sent from the programmer are not accepted.
The ID code consists of 8-bit data, the areas of which, beginning with the first byte, are 0FFFDF
0FFFE3 , 0FFFEB
16
codes are preset at these addresses and write it in the flash memory.
Figure 1.22.3 shows the ID code store addresses.
Rev.1.00 2003.05.30 page 260
pins, the microcomputer is placed in boot mode, thereby executing the program in
0
" (ROM code protect removed), the flash memory can be read or rewritten. Once the
2
, 0FFFEF , 0FFFF3 , 0FFFF7
16 16 16
, and 0FFFFB . Prepare a program in which the ID
16 16
Flash Memory
pin and a high-level
5
,
16