AN1176 STMicroelectronics, AN1176 Datasheet - Page 20

• Manufacturer Part Number: AN1176
• Description: 68HC11/PSD813F1 DESIGN GUIDE
• Manufacturer: STMicroelectronics

3.2.1 Memory Map Configuration at Boot-Up/ISP
Figure 5 shows how the memory map looks at system power-on or at system reset. The SWAP
bit is one of the eight internal PSD page register bits, whose value is zero by default. The SWAP
bit is an example of how the page register bits can be implemented for uses other than memory
paging. Here’s what the 68HC11 does upon power-up or reset:
Setting the SWAP bit maps EEPROM segments EES0/EES1 out of the MCU boot area and maps
in a segment of main flash memory, FS7, in its place as shown in Figure 6. This swapping action
is implemented by including the SWAP bit in the PSDabel equations for the memory chip select
equations.
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Boot from EEPROM (EES0/EES1) at address FFFEh
Perform a checksum of main flash memory
Download main flash memory from a host computer if needed and validate contents
Perform an execution jump from EEPROM to main flash segment FS0
Set the SWAP bit to logic one.
(any page )
C O M M O N
R EG IO N
R EG IO N
PAG ED
Figure 5 – Memory Map, Enhanced Design at Boot-Up/ISP
F FF F
C 00 0
8A00
8B00
820 0
800 0
400 0
000 0
900 0
RS O , 2K bytes S R A M
CS IO P, P S D C ontrol
68H C11 Regs/RAM
MEMO RY MAP BEFORE SW APPING ISP LO ADER CODE
S ystem boots in this config uration from reset o r po wer-on
SYS T EM I/O
EES1
E E P R O M
EES0
E E P R O M
12K bytes
16K bytes
16K bytes
8K bytes
8K bytes
FS0
FS2
FS1
000 0
F lash
F lash
F lash
PAG E 0
000 0
16K bytes
16K bytes
FS4
FS3
F lash
F lash
PAG E 1
1) S W A P b it = 0 (default).
2) M C U b oots from E E S0 /E E S 1.
3) M C U ru ns checksum of m ain flash.
4) M C U d ownlo ads m ain fla sh if nee ded.
5) M C U e xe cu tion jum ps to FS 0
6) M C U sets SW A P bit = 1.
800 0
16K bytes
16K bytes
FS6
FS5
F lash
F lash
PAG E 2
800 0
EES2
E E P R O M
16K bytes
EES3
8K bytes
E E P R O M
FS7
8K bytes
F lash
PAG E 3
800 0
400 0
200 0
000 0