DS2155 datasheet(173/262 Pages) DALLAS

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DS2156

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Figure 24-4 shows an example where the ATM must pause the data transmission, since it has no data

available (in this case, for three clock cycles). This is done by deasserting UT-ENB and (optionally)

setting UT-DATAx and UT-SOC into a high-impedance state. Polling can continue. In the last clock

cycle before restarting the transmission, the address “M” of the previously selected PHY is put on the

UT-ADDRx bus to reselect PHY M again.

Figure 24-4. Transmission to PHY Paused for Three Cycles

24.5.2

UTOPIA Side Transmit: Direct Status Mode (Multitransmit CLAV)

The DS2156 supports direct status mode per [3] for a maximum of four PHY ports connected to one

ATM layer. For each PHY port, the status signals UR-CLAV and UT-CLAV are permanently available

according to UTOPIA Level 1 specification. PHY devices with up to four PHY ports on-chip have up to

four UR-CLAV and up to four UT-CLAV status signals, one pair of UR-CLAV and UT-CLAV for each

PHY port.

Status signals and cell transfers are independent of each other. No address information is needed to obtain

status information. Address information must be valid only for selecting a PHY port prior to one or

multiple cell transfers. With respect to the status signals UR-CLAV and UT-CLAV, this mode of

operation corresponds to that of four individual PHY devices according to UTOPIA Level 1. With respect

to the cell transfer, this mode of operation corresponds to that as described in other parts of this

document. The ATM layer selects a PHY port for cell transfer by placing the desired port on the address

lines (UR-ADDRx, UT-ADDRx), while the enable signal (UR-ENB, UT-ENB) is deasserted. All PHY

ports examine only the value on the address lines for possible selection when the enable signal is

deasserted. In case the ATM suspends transmission for a specific PHY port during a cell transfer, no cells

to/from other PHY ports can be transferred during this time.

N+1

N-4

N+2

N+3

N+1

N-4

N+2

N+3

P31 P32 P33 P34

P35 P36

P38 P39

P37

UT-CLK

UT-ADDRx

UT-CLAV

UT-ENB

UT-DATAx

UT-SOC

CELL XMIT TO:

PHY M

POLLING

PHY M

PAUSE

XMIT

POLLING

SELECTION

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