W741E260 Datasheet, PDF (11/94 Pages) Winbond – 4-BIT FLASH MICROCONTROLLER

W741E260
2. X011B → X000B: Enabling the main-oscillator (Fm) should not be done simultaneously with
changing the FOSC from Fs into Fm. The main-oscillator (Fm) should be enabled first before a delay
subroutine is called to allow the main-oscillator to oscillate stably. The FOSC can now be changed
from Fs into Fm. The correct sequence is therefore X011B→X001B→delay subroutine→X000B.
The suggested delay for Fm is 20 mS for 455 KHz ceramic resonator and 10 mS for 4 MHz crystal.
We must remember that the X010B state is inhibitive, because it will induce a system shutdown.
The organization of the dual-clock operation mode is shown below.
Mask Option (High/Low Freq.)
HOLD
SCR.0
XIN1
XOUT1
Main Oscillator
Fm
Fs
Fosc _{System Clock}
Generator
T1
T2
T3
SCR.1 _{enable/disable}
T4
Divider 0
XIN2
XOUT2
Sub-oscillator
Mask Option
(Single/Dual Clock) _{enable/disable}
Fosc/32
Fosc
Mask Option (High/Low Freq.)
LCD Frequency
Selector
FLCD
Mask Option (Single/Dual Clock)
Divider 1
INT4
HCF.4
SCR.3 (14/13 bit)
SCR
Figure 4. The Dual Clock Operation Mode Control Diagram
3
2
1
0
W
W
W
Note: W means write only.
Bit 0 = 0 Main oscillator is selected (Fosc = Fm)
= 1 Sub-oscillator is selected (Fosc = Fs)
Bit 1 = 0 Enable Fm
= 1 Disable Fm
Bit 2
Reserved
Bit 3 = 0 14-bit Divider1 is selected
= 1 13-bit Divider1 is selected
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Publication Release Date: March 1998
Revision A2