Rev. 1.10
108
November 26, 2019
Rev. 1.10
109
November 26, 2019
HT68FB240
USB Low Speed Flash MCU
USB Interface
The USB interface is a
4
-wire serial bus that allows communication between a host device and up
to 127 max peripheral devices on the same bus. A token based protocol method is used by the host
device for communication control. Other advantages of the USB bus include live plugging and
unplugging and dynamic device configuration. As the complexity of USB data protocol does not
permit comprehensive USB operation information to be provided in this datasheet, the reader should
therefore consult other external information for a detailed USB understanding.
The device includes a USB interface function allowing for the convenient design of USB peripheral
products.
Power Plane
There is one power plane for HT68FB
240: UBUS/VDD.
For
the
UBUS/VDD
will supply all the HT68FB240 circuits includ
ing
USB SIE and be sourced
from pin "UBUS/VDD". Once the USB is
removed from
the USB and there is no power in the
UBUS/VDD pin, the HT68FB240 circuit is no longer operation
al.
USB Suspend Wake-Up Remote Wake-Up
If there is no signal on the USB bus for over 3ms, the device will go into a suspend mode. The
Suspend flag, SUSP, in the USC register, will then be set high and an USB interrupt will be
generated to indicate that the device should jump to the suspend state to meet the requirements of the
USB suspend current spec. In order to meet the requirements of the suspend current, the firmware
should disable the USB clock by clearing the USBCKEN bit to "0".
The suspend current can be further decreased by setting the SUSP2 bit in the UCC register. When
the resume signal is sent out by the host, the device will be woken up the by the USB interrupt and
the RESUME bit in the USC register will be set. To ensure correct device operation, the program
must set the USBCKEN bit in the UCC register high and clear the SUSP2 bit in the UCC register.
The Resume signal will be cleared before the Idle signal is sent out by the host and the Suspend
line
in the USC register will change to zero. So when the MCU detects the Suspend bit in the USC
register, the condition of the Resume line should be noted and taken into consideration.
SUSPEND
USB Resume Signal
USB_INT
The device has a remote wake up function which can wake-up the USB Host by sending a wake-up
pulse through RMWK in the USC register. Once the USB Host receives a wake-up signal from the
device, it will send a Resume signal to the device.
SUSPEND
USB Resume Signal
USB_INT
RMWK
Min.2.5ms
Min. 1 USB CLK