Hitachi H8/3637 Hardware Manual page 116

Note: * Unpredictable data may be output if this area is read in PROM mode.
When programming with a PROM programmer, be sure to specify addresses
from H'0000 to H'EDFF.
If H'EE00 and higher addresses are programmed by mistake, it may become
impossible to program or verify the PROM. When programming, specify
H'FF for this address area (H'EE00 to H'1FFFF).
108
Address in
MCU mode
H'0000
On-chip PROM
H'EDFF
Unused area
Figure 6.3 Memory Map in PROM Mode
Address in
PROM mode
H'0000
H'EDFF
*
H'1FFFF