UPD78F9234MC-5A4-A Datasheet, PDF (273/419 Pages) Renesas Technology Corp – Old Company Name in Catalogs and Other Documents

CHAPTER 18 OPTION BYTE
Figure 18-2. Format of Option Byte (2/2)
LIOCP
Low-speed internal oscillates
1
Cannot be stopped (oscillation does not stop even if 1 is written to the LSRSTOP bit)
0
Can be stopped by software (oscillation stops when 1 is written to the LSRSTOP bit)
Cautions 1. If it is selected that low-speed internal oscillator cannot be stopped, the count clock to
the watchdog timer (WDT) is fixed to low-speed internal oscillation clock.
2. If it is selected that low-speed internal oscillator can be stopped by software, supply of
the count clock to WDT is stopped in the HALT/STOP mode, regardless of the setting of
bit 0 (LSRSTOP) of the low-speed internal oscillation mode register (LSRCM). Similarly,
clock supply is also stopped when a clock other than the low-speed internal oscillation
clock is selected as a count clock to WDT.
While the low-speed internal oscillator is operating (LSRSTOP = 0), the clock can be
supplied to the 8-bit timer H1 even in the STOP mode.
Remarks 1. ( ): fX = 10 MHz
2. For the oscillation stabilization time of the resonator, refer to the characteristics of the resonator
to be used.
3. An example of software coding for setting the option bytes is shown below.
OPB OSEG AT 0080H
DB 10010001B
; Set to option byte
; Low-speed internal oscillator cannot be stopped
; The system clock is a crystal or ceramic resonator.
; The RESET pin is used as an input-only port pin (P34).
; Minimum oscillation stabilization time (2¹⁰/fX)
4. For details on the timing at which the option byte is referenced, see CHAPTER 15 RESET
FUNCTION.
18.3 Caution When the RESET Pin Is Used as an Input-Only Port Pin (P34)
Be aware of the following when re-erasing/-writing (by on-board programming using a dedicated flash memory
programmer) an already-written device which has been set as “The RESET pin is used as an input-only port pin
(P34)” by the option byte function.
Before supplying power to the target system, connect a dedicated flash memory programmer and turn its power on.
If the power is supplied to the target system beforehand, the flash memory programming mode cannot be switched
to.
User’s Manual U17446EJ5V0UD
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