HD64F2168 Datasheet, PDF (708/874 Pages) Renesas Technology Corp – Renesas 16-Bit Single-Chip Microcomputer

20.6 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 programmer mode.)
1. MAT switching by FMATS should always be executed from the on-chip RAM.
2. To ensure that the MAT that has been switched to is accessible, execute four NOP instructions
in the on-chip RAM immediately after writing to FMATS 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. If interrupt processing is to be the same before and after MAT switching,
transfer the interrupt-processing routines to the on-chip RAM and set the WEINTE bit in
FCCS to place the interrupt-vector table in the on-chip RAM.
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.
<User MAT>
<On-chip RAM>
Procedure for
switching to the
user boot MAT
Procedure for
switching to
the user MAT
<User boot MAT>
Procedure for switching to the user boot MAT
(1) Mask interrupts
(2) Write H'AA to FMATS.
(3) Execute four NOP instructions before
accessing the user boot MAT.
Procedure for switching to the user MAT
(1) Mask interrupts
(2) Write a value other than H'AA to FMATS.
(3) Execute four NOP instructions before accessing
the user MAT.
Figure 20.17 Switching between the User MAT and User Boot MAT
Rev. 3.00, 03/04, page 668 of 830