Format Of Option Byte - NEC 78K0S/KA1+ User Manual

17.2 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 P121 and P122 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 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, P121 cannot be used as an I/O
port pin.
(3) High-speed internal oscillation clock is selected
P121 and P122 can be used as I/O port pins.
× : don't care
Remark
260
CHAPTER 17 OPTION BYTE
Figure 17-2. Format of Option Byte (1/2)
6 5 4
DEFOSTS0 1
Oscillation stabilization time on power application or after reset release
10
µ
0 2 /fx (102.4 s)
12
µ
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 U16898EJ3V0UD
3 2
RMCE OSCSEL1
Control of RESET pin
Selection of system clock source
1 0
OSCSEL0 LIOCP