DP83902AVF datasheet(48/70 Pages) NSC

48 / 70 page

130 Bus Arbitration and Timing (Continued)

An additional caution for high speed systems is that the

polling must follow guidelines specified in the Time Between

Chip Selects section That is there must be at least 4 bus

clocks between chip selects (For example when BSCK e

20 MHz then this time should be 200 ns)

The general flow for executing a Remote Write is

1 Set Remote Byte Count to a value l1 and Remote Start

Address to unused RAM (one location before the trans-

mit start address is usually a safe location)

2 Issue the ‘‘dummy’’ Remote Read command

3 Read the Current Remote DMA Address (CRDA) (both

bytes)

4 Compare to previous CRDA value if different go to 6

5 Delay and jump to 3

6 Set up for the Remote Write command by setting the

Remote Byte Count and the Remote Start Address (note

that if the Remote Byte count in step 1 can be set to the

transmit byte count plus one and the Remote Start Ad-

dress to one less these will now be incremented to the

correct values)

7 Issue the Remote Write command

TLF11157 – 62

Note

The dashed lines indicate incorrect timing as described in text

Timing Diagram for Dummy Remote Read

DP83902AVF Datenblatt(PDF) 48 Page - National Semiconductor (TI)