Preliminary User’s Manual U16846EJ1V0UD
332
CHAPTER 20 OPTION BYTE
The 78K0/KB1+ has an area called an option byte at address 0080H of the flash memory. When using the
product, be sure to set the following functions by using the option byte.
(1) Selection
of
high-speed system clock oscillation
•
Crystal/ceramic oscillator
•
External RC oscillator
(2) Ring-OSC
•
Cannot be stopped.
•
Can be stopped by software.
Figure 20-1. Allocation of Option Byte
Option byte
–
–
Flash memory
–
–
–
–
OSCSEL0 RINGOSC
0 0 0 0 H
0 0 8 0 H
Figure 20-2. Format of Option Byte
Address: 0080H
7 6 5 4 3 2 1 0
−
−
−
−
−
−
OSCSEL0 RINGOSC
OSCSEL0
High-speed
system
clock oscillation selection
0
Crystal/ceramic
oscillation
1
External RC oscillation
RINGOSC
Ring-OSC
oscillation
0
Can be stopped by software
1
Cannot
be
stopped
Cautions 1. Select crystal/ceramic oscillation or external RC oscillation when using an external clock.
2. To use the boot swap function, be sure to store the option data in the boot cluster 1 (for the
boot swap function, see 21.8 Boot Swap Function).
3. Be sure to clear bits 2 to 7 to 0.
Remark An example of software coding for setting the option bytes is shown below.
OPT
CSEG
AT
0080H
OPTION:
DB
03H
; Set to option byte (external RC oscillation used/
Ring-OSC
cannot
be
stopped)