Espressif ESP32 Technical Reference Manual page 266

10 Ethernet Media Access Controller (MAC)
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EMACRETRY When this bit is set, the MAC attempts only one transmission. When a collision occurs
on the MII interface, the MAC ignores the current frame transmission and reports a Frame Abort
with excessive collision error in the transmit frame status. When this bit is reset, the MAC attempts
retries based on the settings of the BL field (Bits [6:5]). This bit is applicable only in the half-
duplex mode. (R/W)
EMACPADCRCSTRIP When this bit is set, the MAC strips the Pad or FCS field on the incoming frames
only if the value of the length field is less than 1,536 bytes. All received frames with length field
greater than or equal to 1,536 bytes are passed to the application without stripping the Pad or
FCS field. When this bit is reset, the MAC passes all incoming frames, without modifying them,
to the Host. (R/W)
EMACBACKOFFLIMIT The Back-Off limit determines the random integer number (r) of slot time de-
lays (512 bit times for 10/100 Mbps) for which the MAC waits before rescheduling a transmission
attempt during retries after a collision. This bit is applicable only in the half-duplex mode.
• 00: k= min (n, 10).
• 01: k = min (n, 8).
• 10: k = min (n, 4).
• 11: k = min (n, 1), n = retransmission attempt. The random integer r takes the value in the
range 0 ~ 2000.
EMACDEFERRALCHECK Deferral Check. (R/W)
EMACTX When this bit is set, the transmit state machine of the MAC is enabled for transmission on
the MII. When this bit is reset, the MAC transmit state machine is disabled after the completion
of the transmission of the current frame, and does not transmit any further frames. (R/W)
EMACRX When this bit is set, the receiver state machine of the MAC is enabled for receiving frames
from the MII. When this bit is reset, the MAC receive state machine is disabled after the com-
pletion of the reception of the current frame, and does not receive any further frames from the
MII. (R/W)
PLTF These bits control the number of preamble bytes that are added to the beginning of every
Transmit frame. The preamble reduction occurs only when the MAC is operating in the full-duplex
mode. 2'b00: 7 bytes of preamble. 2'b01: 5 bytes of preamble. 2'b10: 3 bytes of preamble.
(R/W)
Espressif Systems
Register 10.15. EMACCONFIG_REG (0x1000)
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