Two Port 10/100 Managed Ethernet Switch with 16-Bit Non-PCI CPU Interface

Datasheet

8.5Host Interface Timing

This section details the characteristics and special restrictions of the various supported host cycles. For detailed timing specifications on supported PIO read/write operations, refer to Section 15.5, "AC Specifications". The LAN9311/LAN9311i supports the following host cycles:

Read Cycles:

„PIO Reads (nCS or nRD controlled)

„PIO Burst Reads (nCS or nRD controlled)

„RX Data FIFO Direct PIO Reads (nCS or nRD controlled)

„RX Data FIFO Direct PIO Burst Reads (nCS or nRD controlled)

Write Cycles:

„PIO Writes (nCS or nWR controlled)

„TX Data FIFO Direct PIO Writes (nCS or nWR controlled)

8.5.1Special Situations

8.5.1.1Reset Ending During a Read Cycle

If a reset condition terminates during an active read cycle, the tail end of the read cycle will be ignored by the LAN9311/LAN9311i.

8.5.1.2Reset Ending Between Halves of a 16-Bit Read Pair

Some registers are readable during reset. The reset condition may terminate between halves of a 16- bit read pair. In this case, the LAN9311/LAN9311i does not require 16-bit read to complete the DWORD cycle. Reads to other registers during reset are not supported, and may lead to unintended behavior.

8.5.1.3Writes Following a Reset

Following any reset, writes from the host bus are ignored until after a read cycle is performed.

8.5.2Special Restrictions on Back-to Back Write-Read Cycles

It is important to note that there are specific restrictions on the timing of back-to-back host write-read operations. These restrictions concern reading the host control registers after any write cycle to the LAN9311/LAN9311i. In some cases there is a delay between writing to the LAN9311/LAN9311i, and the subsequent side effect (change in the control register value). For example, when writing to the TX Data FIFO, it takes up to 135ns for the level indication to change in the TX FIFO Information Register (TX_FIFO_INF).

In order to prevent the host from reading stale data after a write operation, minimum wait periods have been established. These periods are specified in Table 8.1. The host processor is required to wait the specified period of time after any write to the LAN9311/LAN9311i before reading the resource specified in the table. These wait periods are for read operations that immediately follow any write cycle. Note that the required wait period is dependant upon the register being read after the write.

Performing “dummy” reads of the Byte Order Test Register (BYTE_TEST) register is a convenient way to guarantee that the minimum write-to-read timing restriction is met. Table 8.1 shows the number of dummy reads that are required before reading the register indicated. The number of BYTE_TEST reads in this table is based on the minimum timing for Tcyc (45ns). For microprocessors with slower busses the number of reads may be reduced as long as the total time is equal to, or greater than the time specified in the table. Note that dummy reads of the BYTE_TEST register are not required as long as the minimum time period is met.

Revision 1.4 (08-19-08)

102

SMSC LAN9311/LAN9311i

 

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