LAN9250 datasheet(158/421 Pages) MICROCHIP

158 / 421 page

LAN9250

DS00001913A-page 158

 2015 Microchip Technology Inc.

RX FIFO Size is the remainder of the unallocated FIFO space (16384 bytes – TX FIFO Size). The RX Status FIFO size

is always equal to 1/16 of the RX FIFO size. The RX Status FIFO length is subtracted from the total RX FIFO size with

the remainder being the RX Data FIFO Size.

For example, if TX_FIF_SZ = 6 then:

Total TX FIFO Size = 6144 Bytes (6KB)

TX Status FIFO Size = 512 Bytes (Fixed)

TX Data FIFO Size = 6144 – 512 = 5632 Bytes

RX FIFO Size = 16384 – 6144 = 10240 Bytes (10KB)

RX Status FIFO Size = 10240 / 16 = 640 Bytes (160 RX Status DWORDs)

RX Data FIFO Size = 10240 – 640 = 9600 Bytes

Table 11-10 contains an overview of the configurable TX/RX FIFO sizes and defaults. TABLE 11-11: shows every valid

setting for the TX_FIF_SZ field and the resulting FIFO sizes. Note that settings not shown in this table are reserved and

should not be used.

Note:

The RX Data FIFO is considered full 4 DWORDs before the length that is specified in the HW_CFG register.

TABLE 11-10: TX/RX FIFO CONFIGURABLE SIZES

FIFO

Size Range

Default

TX Status

512

RX Status

128-892

704

TX Data

1536-13824

4608

RX Data

1920-13440

10560

TABLE 11-11: VALID TX/RX FIFO ALLOCATIONS

TX_FIF_SZ

TX DATA

FIFO SIZE (bytes)

TX STATUS

FIFO SIZE (bytes)

RX DATA

FIFO SIZE (bytes)

RX STATUS

FIFO SIZE (bytes)

1536

512

13440

896

2560

512

12480

832

3584

512

11520

768

4608

512

10560

704

5632

512

9600

640

6656

512

8640

576

7680

512

7680

512

8704

512

6720

448

9728

512

5760

384

10752

512

4800

320

11776

512

3840

256

12800

512

2880

192

13824

512

1920

128

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