DS2155 datasheet(180/262 Pages) DALLAS

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DS2156

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An example for the receive direction is shown in Figure 24-11. The status signals UR-CLAVx are

associated to PHY port addresses #4, #3, #2, and #1. There is no need for a unique null device so “X =

don’t care” on the address lines UR-ADDRx.

In Figure 24-11, the polling of PHY ports starts while no cell transfer takes place. The ATM layer

monitors all four status signals UR-CLAVx. At clock edge #3 it detects a cell available at PHY port #1,

UR-CLAV(1) asserted. It selects that PHY port by placing address #1 on the address lines with rising

clock edge #3. PHY port #1 detects this at clock edge #4. At clock edge #5, PHY port #1 detects

UR-ENB asserted, thus cell transfer for PHY port #1 starts with rising clock edge #5.

At clock edge #5 the ATM layer detects a cell available at PHY port #3, UR-CLAV(3) asserted. Not

knowing whether PHY port #1 may have another cell available or not, the ATM layer deselects PHY port

#1 and selects PHY port #3 for cell transfer with rising clock edge #57 by placing address #3 on the

address lines and deasserting UR-ENB. PHY port #1 and PHY port #3 detect this at clock edge #58. At

clock edge #59, PHY port #3 detects UR-ENB asserted, thus cell transfer starts with rising clock edge

#59. At clock edge #111, no cell is available at PHY ports #1, #2, and #4. The ATM layer keeps

UR-ENB asserted and detects at clock edge #113 the first byte of another cell available from PHY port

#3, UR-CLAV(3) asserted. Thus, cell transfer takes place starting with rising clock edge #112. At clock

edge #164, again, no cell is available at PHY ports #1, #2, and #4. The ATM layer keeps the UR-ENB

asserted and also detects at clock edge #166 no cell available from PHY port #3, UR-CLAV(3)

deasserted. Thus, the ATM layer deselects PHY port #3 by deasserting UR-ENB with rising clock edge

#166.

Figure 24-11. Example of Direct Status Indication, Receive Direction

112

113

UR-CLK

UR-ADDRx

UR-CLAV(1)

UR-ENB

UR-SOC

114

P48

UR-DATAx

UR-CLAV(2)

UR-CLAV(3)

UR-CLAV(4)

PORT #1

PORT #2

PORT #3

PORT #4

P48

165

166

167

111

164

P48

Cell Transfer

(port #1)

Cell Transfer

(port #3)

Cell Transfer

(port #3)

DS2155 Datasheet(PDF) 180 Page - Dallas Semiconductor

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