MPC8540 datasheet(679/1302 Pages) FREESCALE

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Memory Map/Register Definition

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

Freescale Semiconductor

14-53

14.5.3.6.4 Half-Duplex Register (HAFDUP)

The HAFDUP register is written by the user. Figure 14-38 shows the HAFDUP register.

Table 14-36 describes the fields of the HAFDUP register.

131415

000

Alternate BEB

Truncation

Alt

BEB

BP No

BackOff

Excess

Defer

Reset

0000_0000_1010_0001

Retransmission Maximum

000

Collision Window

Reset

1111_0000_0011_0111

Offset

TSEC1:0x2_450C; TSEC2:0x2_550C

Figure 14-38. Half-Duplex Register Definition

Table 14-36. HAFDUP Field Descriptions

Bits

Name

Description

0–7

—

Reserved

8–11

Alternate BEB

Truncation

This field is used while alternate binary exponential back-off enable is set. The value

programmed is substituted for the Ethernet standard value of ten. Its default is 0xA.

Alt BEB

Alternate binary exponential back-off. This bit is cleared by default.

0 The Tx MAC follows the standard binary exponential back-off rule.

1 The Tx MAC uses the alternate binary exponential back-off truncation setting instead of the

802.3 standard tenth collision. The standard specifies that any collision after the tenth uses

one less than 210 (210 – 1) as the maximum back-off time.

BP No BackOff

Back pressure no back-off. This bit is cleared by default.

0 The Tx MAC follows the binary exponential back-off rule.

1 The Tx MAC immediately re-transmits, following a collision, during back pressure

operation.

No BackOff

No back-off. This bit is cleared by default.

0 The Tx MAC follows the binary exponential back-off rule.

1 The Tx MAC immediately re-transmits following a collision.

Excess Defer

Excessively deferred. This bit is set by default.

0 The Tx MAC aborts the transmission of a packet that is excessively deferred.

1 The Tx MAC allows the transmission of a packet that is excessively deferred.

16–19

Retransmission

Maximum

This is a programmable field specifying the number of retransmission attempts following a

collision before aborting the packet due to excessive collisions. The standard specifies the

attempt limit to be 0xF (15d). Its default value is 0xF.

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