ENC28J60
To write to a PHY register:
3.3
PHY Registers
1. Write the address of the PHY register to write to
into the MIREGADR register.
The PHY registers provide configuration and control of
the PHY module, as well as status information about its
operation. All PHY registers are 16 bits in width. There
are a total of 32 PHY addresses; however, only 9 loca-
tions are implemented. Writes to unimplemented
locations are ignored and any attempts to read these
locations will return ‘0’. All reserved locations should be
written as ‘0’; their contents should be ignored when
read.
2. Write the lower 8 bits of data to write into the
MIWRL register.
3. Write the upper 8 bits of data to write into the
MIWRH register. Writing to this register auto-
matically begins the MIIM transaction, so it must
be written to after MIWRL. The MISTAT.BUSY
bit becomes set.
Unlike the ETH, MAC and MII control registers, or the
buffer memory, the PHY registers are not directly
accessible through the SPI control interface. Instead,
access is accomplished through a special set of MAC
control registers that implement Media Independent
Interface Management (MIIM). These control registers
are referred to as the MII registers. The registers that
control access to the PHY registers are shown in
Register 3-3 and Register 3-4.
The PHY register will be written after the MIIM opera-
tion completes, which takes 10.24 μs. When the write
operation has completed, the BUSY bit will clear itself.
The host controller should not start any MIISCAN or
MIIRD operations while busy.
3.3.3
SCANNING A PHY REGISTER
The MAC can be configured to perform automatic
back-to-back read operations on a PHY register. This
can significantly reduce the host controller complexity
when periodic status information updates are desired.
To perform the scan operation:
3.3.1
READING PHY REGISTERS
When a PHY register is read, the entire 16 bits are
obtained.
1. Write the address of the PHY register to read
from into the MIREGADR register.
To read from a PHY register:
2. Set the MICMD.MIISCAN bit. The scan opera-
tion begins and the MISTAT.BUSY bit is set. The
first read operation will complete after 10.24 μs.
Subsequent reads will be done at the same
interval until the operation is cancelled. The
MISTAT.NVALID bit may be polled to determine
when the first read operation is complete.
1. Write the address of the PHY register to read
from into the MIREGADR register.
2. Set the MICMD.MIIRD bit. The read operation
begins and the MISTAT.BUSY bit is set.
3. Wait 10.24 μs. Poll the MISTAT.BUSY bit to be
certain that the operation is complete. While
busy, the host controller should not start any
MIISCAN operations or write to the MIWRH
register.
After setting the MIISCAN bit, the MIRDL and MIRDH
registers will automatically be updated every 10.24 μs.
There is no status information which can be used to
determine when the MIRD registers are updated. Since
the host controller can only read one MII register at a
time through the SPI, it must not be assumed that the
values of MIRDL and MIRDH were read from the PHY
at exactly the same time.
When the MAC has obtained the register
contents, the BUSY bit will clear itself.
4. Clear the MICMD.MIIRD bit.
5. Read the desired data from the MIRDL and
MIRDH registers. The order that these bytes are
accessed is unimportant.
When the MIISCAN operation is in progress, the host
controller must not attempt to write to MIWRH or start
an MIIRD operation. The MIISCAN operation can be
cancelled by clearing the MICMD.MIISCAN bit and
then polling the MISTAT.BUSY bit. New operations may
be started after the BUSY bit is cleared.
3.3.2
WRITING PHY REGISTERS
When a PHY register is written to, the entire 16 bits is
written at once; selective bit writes are not imple-
mented. If it is necessary to reprogram only select bits
in the register, the controller must first read the PHY
register, modify the resulting data and then write the
data back to the PHY register.
© 2006 Microchip Technology Inc.
Preliminary
DS39662B-page 19
MICROCHIP [ MICROCHIP ]
