Product Application Note
■
BCM5221
7/7/00
■
BCM5220
Bro a d c o m Co rp o r a t i o n
5221/5220-AN01 Product Application Note, Revision R
Page 10
Figure 5:
Magnetics Connection and Differential Cable Termination Requirements
M
EDIA
C
ONVERSION
This section describes the ability of the BCM5221 to act as a Media Convertor (100Base-TX <> 100Base-FX). The BCM5221
includes internal receive channel FIFOs to allow the data to cross over the clock boundaries without any requirement for
external buffering or clock multiplexing.
Figure 6 on page 11 illustrates how to implement glueless media conversion using two BCM5221 devices. Note that Auto-
negotiation should be disabled for both of the BCM5221 devices. Additionally, half-duplex operation between the two 5221
devices is not supported. Media Conversion must be implemented in full-duplex. Note that this does not preclude the use of
a BCM5221 media converter in a half-duplex system.
The following pin strapping is required for Media Conversion. Pull-up and pull-down values of 4.7 K
Ω
are recommended.
100BASE-TX PHY:
•
LINKLED#/MEDIA_CONV# (pin 35) must be pulled low
•
MII_EN (pin 18) must be pulled low
•
ANEN (pin 38) must be pulled low
•
F100 (pin 37) must be pulled high or left unconnected
•
FDX (pin 39) must be pulled high
•
SD+ and SD- (pins 21 and 19) must be pulled low or left unconnected
100BASE-FX PHY:
•
LINKLED#/MEDIA_CONV# (pin 35) must be pulled low
•
MII_EN (pin 18) must be pulled low
•
ANEN (pin 38) must be pulled low
•
F100 (pin 37) must be pulled high or left unconnected
•
FDX (pin 39) must be pulled high
•
SD+ and SD- (pins 21 and 19) must be connected as specified in the 100BASE-FX section of this application note.
TDP
BCM5221 PHY
TDN
2.5V
2.5V
1:1
RDP
RDN
49.9
Ω
MDIX Magnetics
2.5V
1:1
49.9
Ω
49.9
Ω
49.9
Ω
2KV, 1nF
0.01uF
RJ45
3
6
2
1
Note that the 49.9
Ω
pull-up resistors and transformer primary center-tap connection
may be pulled- to either 2.5V or 3.3V depending on the application.
