Fast Ethernet Controller (FEC)
Freescale Semiconductor
16-19
MCF51CN128 Reference Manual, Rev. 6
16.4.18 FIFO Receive Bound Register (FRBR)
FRBR indicates the upper address bound of the FIFO RAM. Drivers can use this value, along with the
FRSR, to appropriately divide the available FIFO RAM between the transmit and receive data paths.
16.4.19 FIFO Receive Start Register (FRSR)
FRSR indicates the starting address of the receive FIFO. FRSR marks the boundary between the transmit
and receive FIFOs. The transmit FIFO uses addresses from the start of the FIFO to the location four bytes
before the address programmed into the FRSR. The receive FIFO uses addresses from FRSR to FRBR
inclusive.
Hardware initializes the FRSR register at reset. FRSR only needs to be written to change the default value.
Table 16-20. TFWR Field Descriptions
Field
Description
31–2
Reserved, must be cleared.
1–0
TFWR
Number of bytes written to transmit FIFO before transmission of a frame begins
00 64 bytes written
01 64 bytes written
10 128 bytes written
11 192 bytes written
Offset: 0x14C
Access: User read-only
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
R 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
R_BOUND
0
0
W
Reset 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0
0
0
Figure 16-19. FIFO Receive Bound Register (FRBR)
Table 16-21. FRBR Field Descriptions
Field
Description
31–10
Reserved, read as 0 (except bit 10, which is read as 1).
9–2
R_BOUND
Read-only. Highest valid FIFO RAM address.
1–0
Reserved, read as 0.
Offset: 0x150
Access: User read/write
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
R 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
R_FSTART
0
0
W
Reset 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0
0
0
Figure 16-20. FIFO Receive Start Register (FRSR)