Rev. 1.10
50
November 26, 2019
Rev. 1.10
51
November 26, 2019
HT68FB240
USB Low Speed Flash MCU
External RES Circuit
Note: * It is recommended that this component is added for added ESD protection.
** It is recommended that this component is added in environments where power line noise is
significant.
More information regarding external reset circuits is located in Application Note HA0075E on the
Holtek website.
Pulling the RES Pin low using external hardware will also execute a device reset. In this case, as in
the case of other resets, the Program Counter will reset to zero and program execution initiated from
this point.
RES Reset Timing Chart
Low Voltage Reset – LVR
The microcontroller contains a low voltage reset circuit in order to monitor the supply voltage of the
device and provide an MCU reset should the value fall below a certain predefined level.
LVR Operation
The LVR function is always enabled with a specific LVR voltage V
LVR
. If the supply voltage of
the device drops to within a range of 0.9V~V
LVR
such as might occur when changing the battery,
the LVR will automatically reset the device internally and the LVRF bit in the CTRL register will
also be set to 1. For a valid LVR signal, a low supply voltage, i.e., a voltage in the range between
0.9V~V
LVR
must exist for a time greater than that specified by t
LVR
in the A.C. characteristics. If the
low supply voltage state does not exceed this value, the LVR will ignore the low supply voltage and
will not perform a reset function.
The actual V
LVR
value can be selected by the LVS bits in the LVRC register. If the LVS7~LVS0 bits
are changed to some certain values by the environmental noise or software setting, the LVR will
reset the device after 2~3 LIRC clock cycles. When this happens, the LRF bit in the CTRL register
will be set to 1. After power on the register will have the value of 01010101B. Note that the LVR
function will be automatically disabled when the device enters the power down mode.
Low Voltage Reset Timing Chart