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CHAPTER 3 FUNCTIONAL DESCRIPTION
User’s Manual S14054EJ4V0UM
55
Table 3-5. CLKS Bit of MIIC Register and Frequency of HCLK
CLKS Bit of MIIC
Bit 3
Bit 2
Frequency Range of HCLK Input
0
0
Not used
0
1
33 MHz MAX
1
0
50 MHz MAX
1
1
66 MHz MAX
The MDC is output only when a management frame is transmitted or received.
(2) MII management frame data
Figure 3-13 shows the MII management frame structure.
Figure 3-13. MII Management Frame Structure
PHYAD REGAD
(Turn around)
(Start bit)
(Preamble)
(Data)
(Operation)
The
µ
PD98431 automatically generates a preamble and start bit in an MII management frame. The op code is
automatically appended in accordance with reading/writing of a register of the external PHY device. PHYAD and
REGAD indicate the device address of the PHY device and a register address of the PHY device, and the values
set to the FIAD and RGAD fields of the MADR register are appended to PHYAD and REGAD.
Reading from the PHY device is executed when the RSTAT bit of the MCMD register is set to 1. Writing to the
PHY device is executed by writing data to the CTLD field of the MWTD register.
The
µ
PD98431 first outputs serial data from the preamble to REGAD as an MDIO signal, and after turn around,
outputs the data set to the CLTD field of the MWTD register for write access. For read access, serial data is
input from the MDIO signal and is written to the PRSD field of the MRDD register.
(3) Access procedure
The MII management frame is transmitted or received as follows:
First, the BUSY bit of the MIND register is checked to see if MII management access is currently in progress. If
the BUSY bit is ON, the
µ
PD98431 waits until it turns OFF. Next, the device address of the targeted external
PHY device and the register address of the PHY device are written to the FIAD and RGAD fields of the MADR
register, respectively.
A write access is started by writing data to the CTLD field of the MWTD register. The BUSY bit turns ON when
data has been written to the MWTD register, and turns OFF when the write access has been completed.
A read access is started when the RSTAT bit of the MCMD register is set to 1. When the RSTAT bit is set to 1,
the BUSY bit turns ON. It turns OFF after the read access has been completed. The host system can obtain the
read data by reading the PRSD field of the MRDD register after confirming that the BUSY bit has turned OFF.