88e3015 Marvell Semiconductor, Inc., 88e3015 Datasheet - Page 47

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

2.12 Automatic and Manual Impedance Calibration
2.12.1 MAC Interface Calibration Circuit
The auto calibration is available for the MAC interface I/Os. The PHY runs the automatic calibration circuit with a
49 ohm impedance target by default after hardware reset. Other impedance targets are available by changing the
impedance target and restarting the auto calibration through register writes. Individual NMOS and PMOS output
transistors could be controlled for 38 to 80 ohm targets in various increments.
Manual NMOS and PMOS settings are available if the automatic calibration is not desired. If the PCB traces are
different from 50 ohms, the output impedance of the MAC interface I/O buffers can be programmed to match the
trace impedance. Users can adjust the NMOS and PMOS driver output strengths to perfectly match the transmis-
sion line impedance and eliminate reflections completely.
2.12.2 MAC Interface Calibration Register Definitions
If Register 29 = 0x000A, then Register 30 is defined as follows:
Table 26:
Copyright © 2006 Marvell
October 26, 2006, Advance
R e g
b it
15
14
13
12:8
7
6
Note
The CRS, COL, and RX_ER pins are not calibrated.
F u n c t i o n
Restart Calibration
Calibration Com-
plete
Reserved
PMOS Value
Reserved
Latch
Register 30 Page 10 - MAC Interface Calibration Definitions
Document Classification: Proprietary Information
S e t t i n g de s c r i p t io n
0 = Normal
1 = Restart
Bit 15 is a self-clearing register. Calibration
will start once the register is cleared.
1 = Calibration complete
0 = Calibration in progress
0
00000 = All fingers off
...
11111 = All fingers on
The automatic calibrated values are stored
here after calibration completes.
Once the LATCH bit is set to 1, the new cal-
ibration value is written. The automatic cali-
brated value is lost.
0
1 = Latch in new value. This bit self clears.
(Used for manual settings)
CONFIDENTIAL
Automatic and Manual Impedance Calibration
M od e
R/W
RO
R/W
R/W
R/W
R/W,
SC
Doc. No. MV-S103657-00, Rev. C
H W
R e s e t
0
0
0
Auto cal-
ibrated
value
0
0
S W
R e s e t
Retain
Retain
Retain
Retain
Retain
Retain
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