88e3015 Marvell Semiconductor, Inc., 88e3015 Datasheet - Page 33

• Manufacturer Part Number: 88e3015
• Description: Integrated 10/100 Fast Ethernet Transceiver
• Manufacturer: Marvell Semiconductor, Inc.

2.4.4 COMA Mode
COMA mode shuts down the PHY into a low power state when it is not being used. When the PHY is in the COMA
mode, the PHY is completely non-functional including register access. COMA mode is entered when the COMAn
pin is set low.
If hardware reset pin (RESETn) and the COMA pin (COMAn) are asserted simultaneously the hardware reset
function has priority over the COMA function.
If the PHY is disabled by removing any one or more of the external power supplies then the COMAn pin has no
functionality. If the PHY is re-enabled then the proper power up sequence must be followed and a hardware reset
applied before the PHY enters into the normal operating state.
If the reference clock (XTAL_IN, XTAL_OUT) stops when the PHY is disabled then the reference clock must be
restarted and hardware reset must be applied before the PHY enters into the normal operating state.
If all external power supplies remain powered up and the reference clock continues to run then the PHY can enter
and exit the COMA state without the need for hardware reset by simply controlling the COMAn pin. If XTAL_IN is
attached to an oscillator instead of a crystal and if the reference clock can be cleanly switched between toggling at
25 MHz and non-toggling state without glitches then the XTAL_IN can be stopped if the relationship shown in
Figure 10
Note that if the power supply and reference clock requirements can be met then all registers will retain their values
during the COMA state.
Figure 10: XTAL_IN to COMAn Relationship
Copyright © 2006 Marvell
October 26, 2006, Advance
can be met. Tstop should be at least 1 ms. Tstart should be at least 0 ms.
XTAL_IN
RESETn
COMAn
Toggling
Document Classification: Proprietary Information
T
stop
CONFIDENTIAL
Not Toggling
Toggling
T
stop
Doc. No. MV-S103657-00, Rev. C
Power Management
Page 33