GD32F20x User Manual
789
MII/RMII bit transmission order
No matter which interface (MII or RMII) is selected, the bit order of transmit/receive is LSB
first.
The deference between MII and RMII is bit number and sending times. MII is low 4bits first
and then high 4bits, but RMII is the lowest 2bits, low 2bits, high 2bits and the highest 2bits.
For example: a byte value is: 10011101b (left to right order: high to low)
Transmission order for MII use 2 cycles: 1101 -> 1001 (left to right order: high to low)
Transmission order for RMII use 4 cycles: 01 -> 11 -> 01 -> 10 (left to right order: high to low)
RMII clock sources
To ensure the synchronization of the clock source, the same clock source is selected for the
MAC and external PHY which is called REF_CLK. The REF_CLK input clock can be
connected to the external 50MHz crystal or microcontroller CK_OUT0 pin. If the clock source
is from CK_OUT0 pin, then the MCU needs to configure the appropriate PLL to ensure the
output frequency of CK_OUT0 pin is 50MHz.
27.3.2.
MAC function overview
MAC module can achieve the following functions:
Data package (transmission and reception)
Frame detecting/decoding and frame boundary delimitation.
Addressing (handling source address and destination address).
Error conditions detect.
Medium access management in Half-duplex mode
Medium allocation (prevent conflicts).
Conflict resolution (dealing with conflicts).
The MAC module can work in two modes
Half-duplex mode: with the CSMA/CD algorithm to contend for using of the physical
medium, at the same time only one transmission direction is active between two stations
is active.
Full-duplex mode: simultaneous transmission and reception without any conflict mode, if
all of the following conditions are satisfied: 1) PHY supports the feature of transmission
and reception operations at the same time. 2) Only two devices connect to the LAN and
the two devices are both configured for Full-duplex mode.
Transmission process of MAC
All transactions are controlled by the dedicated DMA controller and MAC in Ethernet. After
Summary of Contents for GD32F20 Series
Page 191: ...GD32F20x User Manual 191 Bits Fields Descriptions 31 0 TRNDATA 31 0 32 Bit Random data ...
Page 290: ...GD32F20x User Manual 290 conversion is ongoing ...
Page 325: ...GD32F20x User Manual 325 15 0 ALRM 15 0 RTC alarm value low ...
Page 385: ...GD32F20x User Manual 385 ...
Page 523: ...GD32F20x User Manual 523 clears AERR bit by writing 0 to it ...