MPC8540 datasheet(678/1302 Pages) FREESCALE

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MPC8540 PowerQUICC III Integrated Host Processor Reference Manual, Rev. 1

14-52

Freescale Semiconductor

Three-Speed Ethernet Controllers

14.5.3.6.3 Inter-Packet Gap/Inter-Frame Gap Register (IPGIFG)

The IPGIFG register is written by the user. Figure 14-37 shows the IPGIFG register.

Table 14-35 describes the fields of the IPGIFG register.

15 16

23 24 25

R 0

Non-Back-to-Back

Inter-Packet-Gap,

Part 1

Non-Back-to-Back

Inter-Packet-Gap,

Part 2

Minimum IFG

Enforcement

Back-to-Back

Inter-Packet-Gap

Reset

0100_0000_0110_0000_0101_0000_0110_0000

Offset

TSEC1:0x2_4508; TSEC2:0x2_5508

Figure 14-37. IPGIFG Register Definition

Table 14-35. IPGIFG Field Descriptions

Bits

Name

Description

0—

Reserved

1–7

Non-Back-to-Back

Inter-Packet-Gap, Part

Programmable field representing the optional carrier Sense window referenced in

IEEE 802.3/4.2.3.2.1 ‘carrier deference’. If carrier is detected during the timing of

IPGR1, the MAC defers to carrier. If, however, carrier becomes active after IPGR1, the

MAC continues timing IPGR2 and transmits, knowingly causing a collision; thus,

ensuring fair access to medium. Its range of values is 0x00 to IPGR2. Its default is

0x40 (64d) which follows the two-thirds/one-third guideline.

8—

Reserved

9–15

Non-Back-to-Back

Inter-Packet-Gap, Part

Programmable field representing the non-back-to-back inter-packet-gap in bits. Its

default is 0x60 (96d), which represents the minimum IPG of 96 bits.

16–23

Minimum IFG

Enforcement

Programmable field representing the minimum number of bits of IFG to enforce

between frames. A frame is dropped whose IFG is less than that programmed. The

default setting of 0x50 (80d) represents half of the nominal minimum IFG which is 160

bits.

—

Reserved

25–31

Back-to-Back

Inter-Packet-Gap

Programmable field representing the IPG between back-to-back packets. This is the

IPG parameter used exclusively in full-duplex mode and in half-duplex mode if two

transmit packets are sent back-to-back. Set this field to the number of bits of IPG

desired. The default setting of 0x60 (96d) represents the minimum IPG of 96 bits.

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