dp83251 National Semiconductor Corporation, dp83251 Datasheet - Page 16

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

4 0 Modes of Operation
4 3 2 Internal Loopback
The Internal Loopback mode can be used to test the func-
tionality of the PLAYER device and to test the data paths
between the PLAYER and BMAC devices before ring inser-
tion
When in the Internal Loopback mode the PLAYER device
performs the following functions



Figure 2-1 PLAYER Device Block Diagram)
Directs the output data of the Transmitter Block to the
input of the Receiver Block through internal paths (see
Ignores the PMD Data Indicate pins (RXD
Outputs Quiet symbols through the PMD Data Request
pins (TXD
g
) and
(Continued)
g
FIGURE 4-2 Internal Loopback
and RXC
g
)
16
The level of the Quiet symbols transmitted through the
TXC
Level bit of the Mode Register
The level of the Quiet symbols transmitted through the
LBD
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 4-2 for a block diagram

Outputs Quiet symbols through the External Loopback
Data pins (LBD
g
g
pins is always high regardless of the Transmit Quiet
pins is programmable through the Transmit Quiet
g
)
TL F 10386 – 16