Rev. 1.10
40
November 26, 2019
Rev. 1.10
41
November 26, 2019
HT68FB240
USB Low Speed Flash MCU
Control Register
A single register, SMOD, is used for overall control of the internal clocks within the device.
SMOD Register
Bit
7
6
5
4
3
2
1
0
Name
CKS2
CKS1
CKS0
—
LTO
HTO
IDLEN
HLCLK
R/W
R/W
R/W
R/W
—
R
R
R/W
R/W
POR
0
0
0
—
0
0
1
1
Bit 7~5
CKS2~CKS0:
The system clock selection when HLCLK is "0"
000: f
L
(f
LIRC
)
001: f
L
(f
LIRC
)
010: f
H
/64
011: f
H
/32
100: f
H
/16
101: f
H
/8
110: f
H
/4
111: f
H
/2
These three bits are used to select which clock is used as the system clock source. In
addition to the system clock source, which can be LIRC, a divided version of the high
speed system oscillator can also be chosen as the system clock source.
Bit 4
Unimplemented, read as "0"
Bit 3
LTO:
Low speed system oscillator ready flag
0: Not ready
1: Ready
This is the low speed system oscillator ready flag which indicates when the low speed
system oscillator is stable after power on reset or a wake-up has occurred. The flag
will be low when in the SLEEP0 Mode but after a wake-up has occurred, the flag will
change to a high level after 2 clock cycles if the LIRC oscillator is used.
Bit 2
HTO:
High speed system oscillator ready flag
0: Not ready
1: Ready
This is the high speed system oscillator ready flag which indicates when the high speed
system oscillator is stable. This flag is cleared to "0" by hardware when the device is
powered on and then changes to a high level after the high speed system oscillator is
stable. Therefore this flag will always be read as "1" by the application program after
device power-on. The flag will be low when in the SLEEP or IDLE0 Mode but after a
wake-up has occurred, the flag will change to a high level after
32
clock cycles if the
HIRC oscillator is used.
Bit 1
IDLEN:
IDLE Mode control
0: Disable
1: Enable
This is the IDLE Mode Control bit and determines what happens when the HALT
instruction is executed. If this bit is high, when a HALT instruction is executed the
device will enter the IDLE Mode. In the IDLE1 Mode the CPU will stop running
but the system clock will continue to keep the peripheral functions operational, if
FSYSON bit is high. If FSYSON bit is low, the CPU and the system clock will all stop
in IDLE0 mode. If the bit is low the device will enter the SLEEP Mode when a HALT
instruction is executed.
Bit 0
HLCLK:
system clock selection
0: f
H
/2 ~ f
H
/64 or f
L
1: f
H
This bit is used to select if the f
H
clock or the f
H
/2~f
H
/64 or f
L
clock is used as the
system clock. When the bit is high the f
H
clock will be selected and if low the
f
H
/2~f
H
/64 or f
L
clock will be selected. When system clock switches from the f
H
clock
to the f
L
clock and the f
H
clock will be automatically switched off to conserve power.