
14 of 24
September 11, 2000
IDT77105
The TxCell and RxCell counters are sized (16 bits) to provide a full
cell count (without roll over) if the counter is read once/second. The
Symbol Error counter and HEC Error counter were given sufficient size
to indicate exact counts for low error-rate conditions. If these counters
overflow, a gross condition is occurring, where additional counter resolu-
tion does not provide additional diagnostic benefit.
Reading Counters
1. Decide which counter value is desired. Write to register 0x06 to
the bit location corresponding to the desired counter. This loads
the Counter Read registers with the selected counter’s value, and
resets this counter to zero.
Note:
Only one counter (Selected bit in 0x06) may be
enabled at any time.
2. Read registers 0x04 (low byte) and 0x05 (high byte) to get the
value.
Further reads may be accomplished in the same manner by first
writing to register 0x06.
Multi-Phy Operation
Multiple 77105's may be connected to a common bus when a multi-
PHY system architecture is needed.
Both Transmit and Receive UTOPIA busses, as well as the utility
bus, can attach to common busses.
Device selection is controlled via the UTOPIA “enable” control
signals: TxEnb and RxEnb. In transmit, TxEnb tells the selected device
that the data and control signals it sees are to be used for ATM cell
transmission. In receive, when RxEnb is deasserted (high), RxData[7:0],
RxParity, and RxSOC are all tri-stated, allowing them to share a
common bus. When RxEnb is asserted, the selected device drives these
outputs, transferring the data to the upstream hardware.
Note that while multiple transmit devices may be selected (e.g. for
multicast) by asserting more than one TxEnb, multiple receive devices
should not be enabled. Also, the output of RxRef is not affected by
RxEnb; the same is also true for TxRef and TxEnb. These must be
routed and/or multiplexed separately.
Figure 12 is an example of connecting multiple PHYs in the transmit
direction. A separate TxEnb and TxClav signal is provided to each
77105 for device select.
Multi-Phy Receive is constructed in the same manner as transmit, in
that each device has dedicated RxEnb and RxClav signals. (See Figure
13).
Figure 12 Multi-PHY: Transmit Example
Figure 13 Multi-PHY Receive Example
"Upstream"
Hardware
77105#1
Magnetics
77105#2
77105#3
77105#4
"UTOPIA Transmit Bus"
-TxData[7:0]
-TxParity
-TxSOC
TxEnb #1
TxCLAV #2
TxEnb #2
TxCLAV #3
TxEnb #3
TxCLAV #4
TxEnb #4
3445 drw 15
Magnetics
Magnetics
Magnetics
2
2
2
2
2
2
2
2
10
10
10
10
10
TxCLAV #1
"Upstream"
Hardware
77105#1
Magnetics
77105#2
77105#3
77105#4
"UTOPIA Receive Bus"
-RxData[7:0]
-RxParity
-RxSOC
RxEnb #1
RxCLAV #2
RxEnb #2
RxCLAV #3
RxEnb #3
RxCLAV #4
RxEnb #4
3445 drw 16
Magnetics
Magnetics
Magnetics
2
2
2
2
2
2
2
2
10
10
10
10
10
RxCLAV #1