D12320VF25V Datasheet, PDF (778/1146 Pages) Renesas Technology Corp – Old Company Name in Catalogs and Other Documents

Section 17 ROM
17.27 Switching between User MAT and User Boot MAT
It is possible to alternate between the user MAT and user boot MAT. However, the following
procedure is required because these MATs are allocated to address 0.
(Switching to the user boot MAT disables programming and erasing. Programming of the user
boot MAT should take place in boot mode or PROM mode.)
(1) MAT switching by the FMATS register should always be executed from the on-chip RAM.
(2) To ensure that the MAT that has been switched to is accessible, execute 4 NOP instructions in
the on-chip RAM immediately before or after writing to the FMATS register of the on-chip
RAM (this prevents access to the flash memory during MAT switching).
(3) If an interrupt has occurred during switching, there is no guarantee of which memory MAT is
being accessed. Always mask the maskable interrupts before switching between MATs. In
addition, configure the system so that NMI interrupts do not occur during MAT switching.
(4) After the MATs have been switched, take care because the interrupt vector table will also have
been switched. Methods for processing the same interrupt before and after MAT switching
include the following:
• Prepare the same interrupt processing routines and interrupt vectors in both the user MAT and
user boot MAT.
• Transfer the interrupt processing routines to on-chip RAM beforehand and set the interrupt
vectors to the same on-chip RAM addresses for both the user MAT and user boot MAT.
(5) Memory sizes of the user MAT and user boot MAT are different. When accessing the user
boot MAT, do not access addresses above the top of its 8-kbyte memory space. If access goes
beyond the 8-kbyte space, the values read are undefined.
Rev.7.00 Feb. 14, 2007 page 744 of 1108
REJ09B0089-0700