DS80C410 Datasheet, PDF (68/102 Pages) Dallas Semiconductor – Network Microcontrollers with Ethernet and CAN

DS80C410/DS80C411 Network Microcontrollers with Ethernet and CAN
Transmit/Receive Packet Buffer Memory (8kB)
The DS80C410 Ethernet controller uses 8kB of internal SRAM as transmit/receive packet buffer memory. This
SRAM is read/write accessible as data memory by the CPU using the MOVX instruction. The BCU also has access
to this SRAM, and automatically writes/reads packet buffer memory whenever it needs to store or retrieve Ethernet
packet information. The logical MOVX address range of the 8kB SRAM is fixed at FFE000h to FFFFFFh.
When used for Ethernet packet buffer memory, the 8kB SRAM is logically configured into (32) pages of 64 words
each, where a word consists of 4 Bytes. These 32 pages can be dynamically allocated between Ethernet transmit
and receive buffer memory. The five least significant bits of the Ethernet buffer size (EBS; E5h) SFR specify how
many pages are allocated for receive buffer memory. The remaining pages of the 32 are used as transmit buffer
memory. Note that transmit and receive data packets can span multiple pages. The reset default state of the
Ethernet buffer size select bits (EBS.4ñEBS.0) is 00000b, which configures all 32 pages as transmit buffer
memory. As an example, setting EBS.4ñEBS.0 = 10000b would result in pages 0ñ15 (16 pages) being configured
as receive buffer memory and pages 16ñ31 (16 pages) being configured as transmit buffer memory. A setting of
11111b leaves a single page (page 31) for transmit buffer memory and configures pages 0ñ30 (31 pages) as
receive buffer memory. Changing the transmit/receive buffer-size settings flush the contents of the receive buffer
and the receive FIFO. Figure 11 is an illustration of the 8kB buffer memory map and addressing scheme.
Figure 11. Transmit/Receive Data Buffer Memory
RECEIVE
BUFFER
(n PAGES)
8kB INTERNAL SRAM
PAGE 0
PAGE 1
.
.
.
.
.
.
PAGE 1
STATUS WORD (WORD 0)
WORD 1
WORD 2
.
.
.
.
WORD 63
BUFFER SIZE
SETTING
(EBS.4ñEBS.0)
TRANSMIT
BUFFER
(32 - n PAGES)
PAGE (n - 2)
PAGE (n - 1)
PAGE n
.
.
.
PAGE 31
FIXED
PAGE WORD BYTE
EXAMPLE: PAGE 1, WORD 2, BYTE 3
11111111 111 00001 000010 11
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