DM9006 Datasheet, PDF (55/76 Pages) Davicom Semiconductor, Inc. – 10/100 Mbps 2-port Ethernet Switch Controller with General Processor Interface

DM9006
2-port Switch with Processor Interface
9. FUNCTIONAL DESCRIPTION
9.1 Processor bus and memory management function:
9.1.1 Processor Interface
When the bit 7 of IMR is cleared, there is a 64K-
In the general processor mode, the chip selection byte memory space in the DM9006 can be accessed.
is just coming from pin CS#. There are only two This configured type of internal memory is used for
addressing ports through the access of the host testing only. The memory write address (register
interface.
FAh/FBh) and the memory read address (register
One port is the INDEX port and the other is the F4h/F5h) represent the physical memory address of
DATA port. The INDEX port is decoded by the CMD the DM9006 internal memory. It is noted that after the
pin=0 and the DATA by the CMD pin=1. The contents memory had been written by memory write command,
of the INDEX port are the register address of the the switch reset command (bit 6 of register 52h)
DATA port. Before the access of any register, the should be set before normal switch function operation,
address of the register must be saved in the INDEX since the controlled data in internal memory may be
port before.
corrupted.
9.1.2 Direct Memory Access Control
The DM9006 provides DMA capability to simplify
the access of the internal memory. After the setting of
the starting address of the internal memory and then
issuing a dummy read/write command to load the
current data to internal data buffer, the desired
location of the internal memory can be accessed by
the read/write command registers. The memory’s
address will be increased with the size equal to the
current operation mode (i.e. the byte or word mode)
and the data of the next location will be loaded to
internal data buffer automatically. It is noted that the
data of the first access (the dummy read/write
command) in a sequential burst should be ignored
because that the data was the contents of the last
read/write command.
There are two configured types of internal
memory which are controlled by bit 7 of IMR. When
the bit 7 of IMR is set, the internal memory is used for
transmit and receive buffers. The transmit buffer
occupies 8K bytes. And the receive buffer occupies
7.75K bytes. Both the transmit and receive buffer
address need not to be programmed instead that they
are managed by the DM9006 automatically. In
transmit function, after power on reset or each time
after the transmit command is issued (bit 0 of TCR is
set), the next starting transmit buffer address is
loaded. In receive function, the 7.75K-byte receive
buffer can be treated as a continued logic memory
space. The memory address will wrap to address 0 if
the end of address is reached.
9.1.3 Packet Transmission
There are two packets, sequentially named as
index I and index II, can be stored in the TX SRAM at
the same time. The index register 02h controls the
insertion of CRC.
The start address of transmission is 00h and the
current packet is index I after software or hardware
reset. Firstly write data to the TX SRAM using the
DMA port and then write the byte count to byte count
register at index register 0fch and 0fdh. Set the bit 1
of control register. The DM9006 starts to transmit the
index I packet. Before the transmission of the index I
packet ends, the data of the next (index II) packet can
be moved to TX SRAM. After the index I packet ends
the transmission, write the byte count data of the
index II to BYTE_COUNT register and then set the bit
1 of control register to transmit the index II packet.
The following packets, named index I, II, I, II… use
the same way to be transmitted.
9.1.4 Packet Reception
The RX SRAM is a ring data structure. Each
packet has a 4-byte header followed with the data of
the reception packet which CRC field is included. The
format of the 4-byte header is 01h, status,
BYTE_COUNT low, and BYTE_COUNT high. It is
noted that the start address of each packet is in the
proper address boundary which depends on the
operation mode (byte or word mode).
Preliminary datasheet
55
DM9006-13-DS-P01
September 1, 2009