LM3S6950 Luminary Micro, Inc, LM3S6950 Datasheet - Page 385

• Manufacturer Part Number: LM3S6950
• Description: Lm3s6950 Arm Microcontroller
• Manufacturer: Luminary Micro, Inc

15.2.2.5 LED Indicators
15.2.3
15.2.3.1 Ethernet Frame Format
July 25, 2008
The PHY supports two LED signals that can be used to indicate various states of operation of the
Ethernet Controller. These signals are mapped to the LED0 and LED1 pins. By default, these pins
are configured as GPIO signals (PF3 and PF2). For the PHY layer to drive these signals, they must
be reconfigured to their hardware function. See “General-Purpose Input/Outputs (GPIOs)” on page
169 for additional details. The function of these pins is programmable via the PHY layer MR23 register.
Refer to page 425 for additonal details on how to program these LED functions.
MAC Configuration/Operation
Ethernet data is carried by Ethernet frames. The basic frame format is shown in Figure
15-3 on page 385.
Figure 15-3. Ethernet Frame
The seven fields of the frame are transmitted from left to right. The bits within the frame are
transmitted from least to most significant bit.
■
■
■
■
■
■
Preamble
The Preamble field is used by the physical layer signaling circuitry to synchronize with the received
frame’s timing. The preamble is 7 octets long.
Start Frame Delimiter (SFD)
The SFD field follows the preamble pattern and indicates the start of the frame. Its value is
1010.1011.
Destination Address (DA)
This field specifies destination addresses for which the frame is intended. The LSB of the DA
determines whether the address is an individual (0), or group/multicast (1) address.
Source Address (SA)
The source address field identifies the station from which the frame was initiated.
Length/Type Field
The meaning of this field depends on its numeric value. The first of two octets is most significant.
This field can be interpreted as length or type code. The maximum length of the data field is
1500 octets. If the value of the Length/Type field is less than or equal to 1500 decimal, it indicates
the number of MAC client data octets. If the value of this field is greater than or equal to 1536
decimal, then it is type interpretation. The meaning of the Length/Type field when the value is
between 1500 and 1536 decimal is unspecified by the standard. The MAC module assumes
type interpretation if the value of the Length/Type field is greater than 1500 decimal.
Data
Preamble
Bytes
7
SFD Destination Address
Byte
1
Bytes
6
Preliminary
Source Address
Bytes
6
Length/
Bytes
Type
2
LM3S6950 Microcontroller
46 - 1500
Bytes
Data
Bytes
FCS
4
385