RTL8306SD/RTL8306SDM
Datasheet
7.1.3.2
Force Mode Full Duplex Flow Control
For UTP without auto-negotiation ability (GxANeg/GyANeg/P4Aneg is 0), IEEE 802.3x flow control’s
ability can be set to ‘Enabled’ by pins GxEnFC/GyEnFC/P4EnFC on a group basis upon reset, or by
internal registers (Reg.5.10) via SMI on a per-port basis after reset. For example:
• Port 4 will be forced to ‘10Full UTP with forced mode full duplex flow control’ ability, regardless of
the connected device, when P4Mode[1:0]=10, P4Aneg=0, P4Spd100=0, P4Full=1, P4EnFC=1.
• Port 0 will be forced to ‘forced mode full duplex flow control’ ability, regardless of the connected
device, when SetGroup=1, GxFull=1, GxEnFC=1.
Regardless of the flow control mode (IEEE 802.3x full duplex flow control, or forced mode full duplex
flow control), when full duplex flow control is enabled, the RTL8306SD/RTL8306SDM will only
recognize IEEE 802.3x flow control PAUSE ON/OFF frames with DA=01-80-C2-00-00-01,
type=0x8808, OP-code=0x01, PAUSE Time = maximum to zero, and with a good CRC.
If a PAUSE frame is received from any PAUSE flow control enabled port set to DA=01-80-C2-00-00-01,
the corresponding port of the RTL8306SD/RTL8306SDM will stop its packet transmission until the
PAUSE timer times out or another PAUSE frame with zero PAUSE time is received. The
RTL8306SD/RTL8306SDM will not forward any IEEE 802.3x PAUSE frames received from any port.
7.1.3.3
Half Duplex Back Pressure
If pin EnDefer is 1, the RTL8306SD/RTL8306SDM will send a preamble to defer the other station’s
transmission when there is no packet to send. Otherwise, if pin EnDefer is 0, the
RTL8306SD/RTL8306SDM will force a collision with the other station’s transmission when the buffer is
full.
• If pin 48pass1 is 0, the RTL8306SD/RTL8306SDM will always collide with JAM (Continuous
collision).
• If pin 48pass1 is 1, the RTL8306SD/RTL8306SDM will try to forward one packet successfully after
48 forced collisions (48pass1), to avoid the connected repeater being partitioned due to excessive
collisions.
7.1.3.4
NWay Mode
For UTP with auto-negotiation ability, pins GxEnFC/GyEnFC/P4EnFC are effective only in full duplex
mode. Therefore, for UTP in half duplex mode, half duplex back pressure flow control is controlled by
the ENBKPRS pin strap upon hardware reset.
6-Port 10/100Mbps Single-Chip Dual MII/RMII Switch Controller
36
Track ID: JATR-1076-21 Rev. 1.1
REALTEK [ Realtek Semiconductor Corp. ]
