UPD78F9234MC-5A4-A Datasheet, PDF (272/419 Pages) Renesas Technology Corp – Old Company Name in Catalogs and Other Documents

CHAPTER 18 OPTION BYTE
18.2 Format of Option Byte
Format of option bytes is shown below.
Figure 18-2. Format of Option Byte (1/2)
Address: 0080H
7
6
5
4
1
DEFOSTS1 DEFOSTS0
1
3
RMCE
2
OSCSEL1
1
OSCSEL0
0
LIOCP
DEFOSTS1 DEFOSTS0
Oscillation stabilization time on power application or after reset release
0
0
2¹⁰/fx (102.4 μs)
0
1
2¹²/fx (409.6 μs)
1
0
2¹⁵/fx (3.27 ms)
1
1
2¹⁷/fx (13.1 ms)
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
Control of RESET pin
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
Selection of system clock source
0
0
Crystal/ceramic oscillation clock
0
1
External clock input
1
×
High-speed internal oscillation clock
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.
Remark × : don’t care
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User’s Manual U17446EJ5V0UD