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UM10503
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© NXP B.V. 2015. All rights reserved.
User manual
Rev. 2.1 — 10 December 2015
831 of 1441
NXP Semiconductors
UM10503
Chapter 28: LPC43xx/LPC43Sxx Ethernet
Table 609. MAC Flow control register (MAC_FLOW_CTRL, address 0x4001 0018) bit description
Bit
Symbol
Description
Reset
value
Access
0
FCB
Flow Control Busy/Backpressure Activate
This register field can be read by the application (Read), can be set to 1 by the
application with a register write of 1 (Write Set), and is cleared to 0 by the core (Self
Clear). The application cannot clear this type of field, and a register write of 0 to this
bit has no effect on this field.
This bit initiates a Pause Control frame in Full-Duplex mode.
In Full-Duplex mode, this bit should be read as 0 before writing to the Flow Control
register. To initiate a Pause control frame, the Application must set this bit to 1. During
a transfer of the Control Frame, this bit will continue to be set to signify that a frame
transmission is in progress. After the completion of Pause control frame transmission,
the MAC will reset this bit to 0. The Flow Control register should not be written to until
this bit is cleared.
In Half-Duplex mode, when this bit is set (and TFE is set), then backpressure is
asserted by the MAC Core. During backpressure, when the MAC receives a new
frame, the transmitter starts sending a JAM pattern resulting in a collision. This control
register bit is logically ORed with the flow controller input signal for the backpressure
function. When the MAC is configured to Full- Duplex mode, the BPA is automatically
disabled.
0
R/W
1
TFE
Transmit Flow Control Enable
In Full-Duplex mode, when this bit is set, the MAC enables the flow control operation
to transmit Pause frames. When this bit is reset, the flow control operation in the MAC
is disabled, and the MAC will not transmit any Pause frames.
In Half-Duplex mode, when this bit is set, the MAC enables the back-pressure
operation. When this bit is reset, the backpressure feature is disabled.
0
R/W
2
RFE
Receive Flow Control Enable
When this bit is set, the MAC will decode the received Pause frame and disable its
transmitter for a specified (Pause Time) time. When this bit is reset, the decode
function of the Pause frame is disabled.
0
R/W
3
UP
Unicast Pause Frame Detect
When this bit is set, the MAC will detect the Pause frames with the station’s unicast
address specified in MAC Address0 High Register and MAC Address0 Low Register,
in addition to the detecting Pause frames with the unique multicast address. When
this bit is reset, the MAC will detect only a Pause frame with the unique multicast
address specified in the 802.3x standard.
0
R/W
5:4
PLT
Pause Low Threshold
This field configures the threshold of the PAUSE timer at which the input flow control
is checked for automatic retransmission of PAUSE Frame. The threshold values
should be always less than the Pause Time configured in Bits[31:16]. For example, if
PT = 0x100 (256 slot-times), and PLT = 01, then a second PAUSE frame is
automatically transmitted if the flow control signal is asserted at 228 (256 – 28)
slot-times after the first PAUSE frame is transmitted.
00
R/W
6
-
Reserved
0x000
RO