Mitsubishi Motors DS5000TK - Manual (Page 24)

USER’S GUIDE
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Application software always has unrestricted read/write
access to the nonvolatile RAM designated as data
memory. This is the memory that lies above the Partition
address and below the Range address (the non–parti-
tionable configuration of the DS5001 will be addressed
separately). Data memory is read or written using the
MOVX instruction. Only the area designated as pro-
gram memory can not be altered. The key to doing a
“Soft Reload” is to temporarily change the program
memory RAM into data memory. Using an SFR, the ap-
plication software can authorize the Secure Microcon-
troller to temporarily redefine a portion of the program
memory area as data memory. Once this is done, the
new code can be received through a serial port (or other
means) and written into data memory. When the pro-
cess is complete and the new memory is verified as cor-
rect, software converts the RAM back into write–pro-
tected program memory for the duration. As with the
memory map control, there are minor differences be-
tween the DS5000 series and DS5001/DS5002 series
devices in how this is accomplished. Each is described
below.
SOFT RELOAD OF A DS5000 SERIES DEVICE
When application software decides that it should repro-
gram a portion of memory, the software must convert
the target area into data memory. The DS5000 will do
this when software sets the PAA bit (MCON.1) to a logic
1. PAA is the Partition Access Enable. Setting PAA has
two effects. The microcontroller will automatically move
the Partition to 0800h and allow write access to the
Partition control bits PA3–0 (MCON.7–4). At this time,
the software can adjust the Partition, but the new value
will not be used until after PAA is cleared. The Partition
remains at 0800h as long as PAA=1, regardless of the
Partition control bits. This leaves a 2K block of NV RAM
(from 0000–0800h) assigned as program memory.
Apart from this, no other changes take place and soft-
ware continues to operate normally. Caution, make cer-
tain that the code that controls the PAA resides in this
first 2K. When PAA=1, all addresses on the Byte–wide
bus greater than 0800h will be viewed as data memory
and can not be executed even if they were program
memory originally. This gives the software read/write
access to the remaining 6K bytes (Range=8K) or 30K
bytes (Range=32K) of NV RAM on the Byte–wide bus.
At this time, software can begin reloading the target
area of memory. There are two minor variations of this
procedure. First, a user’s loader routine that resides
below 0800h (2K) can reprogram the remainder of
memory as needed. This is done be receiving the new
code through a serial port or other mechanism and writ-
ing it to the RAM at the addresses where it will be
executed. Since the RAM is data memory, the write op-
eration is done using MOVX instructions.
The second option is that the user’s code below 2K can
simply move the Partition to a new value. This is done by
writing a new value for PA3–0 in MCON (MCON.7–4)
while PAA is still set to a 1, then clearing PAA. The pur-
pose of this would be that the loader routine mentioned
in option 1 resides in memory above 2K, but below the
target memory area. To gain access, the Partition must
be moved to a location that includes this loader routine.
Once the Partition is moved to this temporary location,
the software loader can reprogram new code as before.
When loading is complete, the Partition must be either
restored or set to a new value that is appropriate for the
new software. If the PA3–0 bits were not modified, then
the PAA bit can simply be cleared. This will cause the old
Partition to be restored. If the PAA3–0 were modified
during loading or software has grown significantly, then
a new Partition is needed. The PA3–0 bits must be writ-
ten while PAA is set to a 1.
The DS5000FP protects the PAA bit from accidental
modification by requiring a Timed Access procedure.
Timed Access is designed to prevent an out–of–control
program from modifying the PAA bit and crashing the
application. Timed Access is discussed in a later sec-
tion. To summarize the “Soft Reload”, the procedure
goes as follows:
1. Ensure that current program execution is in the
range of 0000h to 0800h.
2. Set the Partition Address Access (PAA) bit using a
Timed Access Procedure.
3. Load new contents into program memory at ad-
dresses above 0800h using MOVX instructions.
4. Define a new Partition address if necessary and
write the appropriate bits into PA3–0 in the MCON
SFR.
5. Restore the current Partition by clearing the PAA bit
with a Timed Access procedure.
6. Resume operation.
The following illustrates the Soft Reload procedure. The
original program requires a partition of 4000h (16K by-
tes). The new program is larger, requiring a Partition of
6000h (24K bytes). The code that performs these steps
is shown below. This routine must be located below
0800h in program memory.