LAN9313 datasheet(119/398 Pages) SMSC

119 / 398 page

Three Port 10/100 Managed Ethernet Switch with MII

Datasheet

SMSC LAN9313/LAN9313i

119

Revision 1.2 (04-08-08)

DATASHEET

The SPI instructions supported by the LAN9313/LAN9313i are listed in Table 8.10. Unsupported

instructions are must not be used.

8.4.1

SPI Read Sequence

The SPI slave interface of the LAN9313/LAN9313i is selected for reads by first bringing nSCS low.

The SI pin should then driven with an 8-bit read instruction, followed by the 8-bit address. On the falling

clock edge which follows the rising edge of the last address bit, the SO output is driven starting with

the msb of the selected register. The remaining register bits are shifted out on subsequent falling clock

edges.

Multiple reads are performed by continuing the clock pulses while nSCS is low. Depending on the

instruction (as shown in Table 8.10), the internal address is incremented, decremented, or maintained.

Maintaining a fixed internal address is useful for register polling. For auto-incrementing instructions,

once the internal address reaches its maximum, it rolls over to 0. For auto-decrementing instructions,

once the internal address reaches 0, it rolls over to its maximum.

The nSCS input is brought high to conclude the cycle. The SO output pin is three-stated at this time.

Since data is read serially, register values are latched (registered) at the beginning of each 32-bit read

to prevent the host from reading an intermediate value. The latching occurs multiple times in a multiple

read sequence. In addition, any register that is affected by a read operation (e.g. a clear on read bit)

is not cleared until after all 32-bits are output. In the event that 32-bits are not read when the nSCS is

returned high, the read is considered invalid and the register is not affected. Multiple registers may be

cleared in a multiple read cycle, each one being cleared as it is read.

SPI reads from unused register addresses return as all zeros.

Table 8.10 Supported SPI Instructions

INSTRUCTION

FORMAT

DESCRIPTION

READ

0000 0011

Read register at the specified address.

Multiple reads maintain the same address.

READ_INC

0000 0111

Read register(s) starting at the specified address.

Multiple reads auto-increment address.

READ_DEC

0000 1011

Read register(s) starting at the specified address.

Multiple reads auto-decrement address.

WRITE

0000 0010

Write register at the specified address.

Multiple writes maintain the same address.

WRITE_INC

0000 0110

Write register(s) starting at the specified address.

Multiple writes auto-increment address.

WRITE_DEC

0000 1010

Write register(s) starting at the specified address.

Multiple writes auto-decrement address.

LAN9313 Datasheet(PDF) 119 Page - SMSC Corporation

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