AN2692 Freescale Semiconductor / Motorola, AN2692 Datasheet - Page 23

• Manufacturer Part Number: AN2692
• Description: MC9S12NE64 Integrated Ethernet Controller
• Manufacturer: Freescale Semiconductor / Motorola

Each EMAC Ethernet buffer is designed to hold only one Ethernet packet at a time. In addition, the EMAC
Ethernet buffer space is user programmable. The following section provides a detailed review of the
EMAC Ethernet buffers.
Buffer Size and Starting Address Mapping (BUFMAP)
The buffer size and starting address mapping data field (BUFMAP) in the Ethernet buffer configuration
register (BUFCFG) allows the user to program the EMAC Ethernet buffer space and specify the ratio
between user RAM and RAM used for the EMAC buffers.
BUFMAP specifies the EMAC Ethernet buffer size configuration options that determine the size of the
MC9S12NE64 receive and transmit Ethernet buffers within system RAM.
The BUFCFG register is shown in
Table 2
settings.
Freescale Semiconductor
•
Read:
Write:
Reset
Two receive buffers — Incoming Ethernet packets store the following data in a receive buffer if a
buffer is available:
–
–
–
–
–
:
provides the configurations for the MC9S12NE64 system RAM usage with the available BUFMAP
Table 2
Destination address
Source address
Type/length
Data
Frame check sequence
15
0
0
BUFMAP
= Unimplemented
14
1
shows that when EMAC Ethernet buffer space is maximized, user RAM is reduced.
0
1
2
3
4
BUFMAP
13
0
Figure 16. Ethernet Buffer Configuration (BUFCFG)
Table 2. EMAC Ethernet Buffer Size and User RAM
MC9S12NE64 Integrated Ethernet Controller, Rev. 0.2
12
0
Buffer Size
Individual
(Bytes)
1.5K
128
256
512
1K
Figure
11
0
0
10
1
16.
9
0
Total Size of EMAC
Ethernet Buffer
Space (Bytes)
384 = 0.375K
768 = 0.75K
1536 = 1.5K
4608 = 4.5K
8
1
3072 = 3K
MC9S12NE64 Ethernet Media Access Controller (EMAC)
7
1
6
1
MAXFL
Remainder RAM for
5
1
User Application
(Bytes)
7.625K
4
0
7.25K
6.5K
3.5K
5K
3
1
2
1
1
1
0
0
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