78Q2123/78Q2133
MicroPHY™
10/100BASE-TX Transceiver
Automatic MDI/ MDI-X Configuration
The 78Q2123/78Q2133 implement the automatic
MDI/MDI-X configuration detailed in IEEE-802.3
2002. This function eliminates the need for cross
over cables when connecting to another device.
When
auto-switching
is
enabled,
the
78Q2123/78Q2133 will attempt to detect activity on
its given configuration. If no activity is seen for
60ms, the device will switch to the other
configuration depending on a random number
sequence. The initial seed of the random number
generator can be set via MR24.3:0. In addition, the
part includes an asynchronous MDIX reset that
varies from 1.29 seconds to 1.57 seconds to ensure
lock step will not occur between two devices.
The 78Q2123/78Q2133 will also allow for auto-
switching while the part is not in auto-negotiation
mode. The IEEE 802.3 specification will not work in
this case if the other device is in auto-negotiation
mode. The 78Q2123/78Q2133 default to auto MDIX
enabled with parallel detection.
Register bits
MR24.6 and MR24.7 are both defaulted to 1. The
78Q2123/78Q2133 will resolve the proper
configuration within 5 seconds.
Page: 6 of 42
©
2009 Teridian Semiconductor Corporation
Rev 1.5
TERIDIAN [ TERIDIAN SEMICONDUCTOR CORPORATION ]
