dp83251 National Semiconductor Corporation, dp83251 Datasheet - Page 17

• Manufacturer Part Number: dp83251
• Description: Player Device Fddi Physical Layer Controller
• Manufacturer: National Semiconductor Corporation

4 0 Modes of Operation
4 3 3 External Loopback
The External Loopback mode can be used to test the func-
tionality of the PLAYER device and to test the data paths
between the PLAYER CRD and BMAC devices before
transmitting and receiving data through the network
When in the External Loopback mode the PLAYER device
performs the following functions

2 PLAYER Device Block Diagram)
Directs the output data of the Transmitter Block to the
external Loopback Data pins (LBD
ly connected to the Clock Recovery Device (see Figure
g
) which are normal-
(Continued)
FIGURE 4-3 External Loopback
17
The level of the Quiet symbols transmitted through the
TXC
Level bit of the Mode Register
If both Internal Loopback and External Loopback modes are
selected Internal Loopback mode will have priority over Ex-
ternal Loopback mode
See Figure 4-3 for a block diagram

Outputs Quiet symbols through the PMD Data Request
pins (TXD
g
pins is programmable through the Transmit Quiet
g
)
TL F 10386 – 17