LAN91C110 datasheet(10/55 Pages) SMSC

10 / 55 page

FEAST Fast Ethernet Controller for PCMCIA and Generic 16-Bit Applications

SMSC DS – LAN91C110 REV. B

Page 10

Rev. 09/05/02

MMU Block

The Hardware Memory Management Unit allocates memory and transmit and receive packet queues. It also determines

the value of the transmit and receive interrupts as a function of the queues. The page size is 2k, with a maximum memory

size of 128k. MIR and MCR values are interpreted in 512 byte units.

BIU Block

The Bus Interface Unit can handle synchronous as well as asynchronous buses; different signals are used for each one.

Transparent latches are added on the address path using rising nADS for latching.

With ISA, the read and write operations are controlled by the edges of nRD and nWR. ARDY is used for notifying the

system that it should extend the access cycle. The leading edge of ARDY is generated by the leading edge of nRD or

nWR while the trailing edge of ARDY is controlled by the internal LAN91C110 clock and, therefore, asynchronous to the

bus.

The BIU is implemented using the following principles:

Address decoding is based on the values of A15-A4 and AEN.

Address latching is performed by using transparent latches that are transparent when nADS=0 and nRD=1, nWR=1

and latch on nADS rising edge.

Byte, word and doubleword accesses to all registers and Data Path are supported except a doubleword write to

offset Ch will only write the BANK SELECT REGISTER (offset Fh).

No bus byte swapping is implemented (no eight bit mode).

Word swapping as a function of A1 is implemented for 16 bit bus support.

The asynchronous interface uses nRD and nWR strobes. If necessary, ARDY is negated on the leading edge of the

strobe. The ARDY trailing edge is controlled by CLK.

MAC-PHY Interface Block

For the MII interface, transmit data is clocked out using the TX25 clock input, while receive data is clocked in using RX25.

In 100 Mbps mode, the LAN91C110 provides the following interface signals to the PHY:

For transmission: TXEN100 TXD0-3 TX25

For reception: RX_DV RX_ER RXD0-3 RX25

For CSMA/CD state machines: CRS100 COL100

A transmission begins by TXEN100 going active (high), and TXD0-TXD3 having the first valid preamble nibble. TXD0

carries the least significant bit of the nibble (that is the one that would go first out of the EPH at 100 Mbps), while TXD3

carries the most significant bit of the nibble. TXEN100 and TXD0-TXD3 are clocked by the LAN91C110 using TX25 rising

edges. TXEN100 goes inactive at the end of the packet on the last nibble of the CRC.

During a transmission, COL100 might become active to indicate a collision. COL100 is asynchronous to the LAN91C110’s

clocks and will be synchronized internally to TX25.

Reception begins when RX_DV (receive data valid) is asserted. A preamble pattern or flag octet will be present at RXD0-

RXD3 when RX_DV is activated. The LAN91C110 requires no training sequence beyond a full flag octet for reception.

RX_DV as well as RXD0-RXD3 are sampled on RX25 rising edges. RXD0 carries the least significant bit and RXD3 the

most significant bit of the nibble. RX_DV goes inactive when the last valid nibble of the packet (CRC) is presented at

RXD0-RXD3.

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