GD32F10x User Manual
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23.4.
Signal description
Table 23-1. USBD signal description
I/O port
Type
Description
VBUS
Input
Bus power port
DM
Input/Output
Differential D-
DP
Input/Output
Differential D+
Note:
As soon as the USBD is enabled, these pins are connected to the USBD internal
transceiver automatically.
23.5.
Clock configuration
According to the USB standard definition, the USB full-speed module adopt fixed 48MHz clock.
It is necessary to configure two clock for using USBD, one is the USB controller clock, its
frequency must be configured to 48MHz, and the other one is the APB1 to USB interface
clock which is also APB1 bus clock, its frequency can be above or below 48MHz.
Note:
In order to meet the system requirements of packet buffer interface and USB data
transfer rate, the frequency of the APB1 bus clock must be greater than 24MHz, so as to
avoid data buffer overflow and underflow.
48MHz clock of USB controller can be generated by dividing MCU internal or external crystal
oscillator by a programmable prescaler, then multiplicating the frequency through PLL.
Regard two frequency division of 8MHz internal oscillator as the input of the PLL, then
12 frequencies doubling the clock.
Regard 8MHz external oscillator as the input of the PLL, firstly frequency doubling, then
adopt USB frequency divider to divide frequency.
When the USB clock is generated by external crystal, only 4 USB frequency prescaler can be
used as 1, 1.5, 2 and 2.5 (2.5 cannot be used, because the frequency of GD32F10x MCU
cannot reach above 108MHz). Thus, for obtaining 48MHz clock, PLL frequencies doubling
can only be 48MHz, 72MHz and 96MHz.
Note:
Regardless of using internal or external crystal oscillator to generate USB clock, the
clock accuracy must reach ±500ppm. If the accuracy of the USB clock cannot meet the
condition, data transfer may not conform to the requirements of the USB specification, and
even it may lead USBD unable to work directly.
Содержание GD32F10 Series
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