Format Of Option Byte - NEC 78K0S/KU1+ User Manual

15.2 Format of Option Byte

Format of option bytes is shown below.
Address: 0080H
7
1 DEFOSTS1
DEFOSTS1 DEFOSTS0
0
0
1
1
Caution The setting of this option is valid only when the crystal/ceramic oscillation clock is selected
as the system clock source. No wait time elapses if the high-speed internal oscillation clock
or external clock input is selected as the system clock source.
RMCE
1 RESET pin is used as is.
0 RESET pin is used as input port pin (P34).
Caution Because the option byte is referenced after reset release, if a low level is input to the RESET
pin before the option byte is referenced, then the reset state is not released.
Also, when setting 0 to RMCE, connect the pull-up resistor.
OSCSEL1 OSCSEL0
0 0
0 1
×
1
Caution Because the X1 and X2 pins are also used as the P23/ANI3 and P22/ANI2 pins, the conditions
under which the X1 and X2 pins can be used differ depending on the selected system clock
source.
(1) Crystal/ceramic oscillation clock is selected
The X1 and X2 pins cannot be used as I/O port pins or analog input pins of A/D converter
because they are used as clock input pins.
(2) External clock input is selected
Because the X1 pin is used as an external clock input pin, P23/ANI3 cannot be used as
an I/O port pin or an analog input pin of A/D converter.
(3) High-speed internal oscillation clock is selected
P23/ANI3 and P22/ANI2 pins can be used as I/O port pins or analog input pins of A/D
converter.
× : don't care
Remark
210
CHAPTER 15 OPTION BYTE
Figure 15-2. Format of Option Byte (1/2)
6 5 4
DEFOSTS0 1
Oscillation stabilization time on power application or after reset release
µ
10
0 2 /fx (102.4 s)
µ
12
1 2 /fx (409.6 s)
15
0 2 /fx (3.27 ms)
17
1 2 /fx (13.1 ms)
Crystal/ceramic oscillation clock
External clock input
High-speed internal oscillation clock
User's Manual U18172EJ2V0UD
3 2
RMCE OSCSEL1
Control of RESET pin
Selection of system clock source
1 0
OSCSEL0 LIOCP