MPC8540 datasheet(1174/1302 Pages) FREESCALE

1174 / 1302 page

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

21-34

Freescale Semiconductor

10/100 Fast Ethernet Controller

Table 21-25 describes the fields of the CRBPTR register.

21.5.3.4.5 Maximum Receive Buffer Length Register (MRBLR)

The MRBLR, shown in Figure 21-27, is written by the user. It informs the FEC how much space

is in the receive buffer pointed to by the RxBD.

Table 21-26 describes the fields of the MRBLR register.

28 29

CRBPTR

Reset

0000_0000_0000_0000_0000_0000_0000_0000

Offset

0x2_6324

Figure 21-26. CRBPTR Register Definition

Table 21-25. CRBPTR Field Descriptions

Bits

Name

Description

0–28

CRBPTR

The CRBPTR register is internally written by the DMA module. The value increments by eight

(bytes) each time a descriptor is read from memory.

29–31

—

Reserved

015 16

25 26

R 0

0000

MRBL

0000

Reset

0000_0000_0000_0000_0000_0000_0000_0000

Offset

0x2_6340

Figure 21-27. MRBLR Register Definition

Table 21-26. MRBLR Field Descriptions

Bits

Name

Description

0–15

—

To ensure that MRBL is a multiple of 64 these bits are reserved and must be cleared.

16–25

MRBL

Maximum receive buffer length. The number of bytes that the FEC receiver writes to the receive

buffer. The MRBL register is written by the user with a multiple of 64 for all modes. The FEC can

write fewer bytes to the buffer than the value set in MRBL if a condition such as an error or

end-of-frame condition occurs, but it never exceeds the MRBL value; therefore, user-supplied

buffers must be at least as large as the MRBL. Note that transmit buffers can have varying lengths

by programming TxBD[Data Length], as needed, and are unaffected by the MRBLR value.

MRBLR is not intended to be changed dynamically while FEC is operating. Change MRBLR only

when the FEC receive function is disabled.

26–31

—

To ensure that MRBL is a multiple of 64 these bits are reserved and must be cleared.

MPC8540 Datasheet(PDF) 1174 Page - Freescale Semiconductor, Inc

MPC8540 Datasheet(HTML) 1174 Page - Freescale Semiconductor, Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL