Rohde & Schwarz RTE - Page 802

Protocol analysis
R&S
®
RTE
802User Manual 1326.1032.02 ─ 20
On physical level, MDIO is a clocked non-return-to-zero (NRZ) code similar to SPI.
According to the Ethernet standard, the protocol defines two threshold levels, 2 V and
0.8 V, which establish a hysteresis.
On logical level, MDIO is a fairly simple protocol with a fixed word length of 64 bits. The
structure of MDIO frames is shown in the following tables:
Table 13-18: MDIO frame structure according to Clause 22
Management Frame Fields
Frame PRE ST OP PHYAD REGAD TA DATA IDLE
WRITE 1...1 01 01 AAAAA RRRRR 10 DDDDDDDDDDDDDDDD Z
READ 1...1 01 10 AAAAA RRRRR Z0 DDDDDDDDDDDDDDDD Z
Table 13-19: MDIO frame structure according to Clause 45
Management Frame Fields
Frame PRE ST OP PRTAD DEVAD TA ADDRESS / DATA IDLE
ADDRESS 1...1 00 00 PPPPP EEEEE 10 AAAAAAAAAAAAAAAA Z
WRITE 1...1 00 01 PPPPP EEEEE 10 DDDDDDDDDDDDDDDD Z
READ 1...1 00 11 PPPPP EEEEE Z0 DDDDDDDDDDDDDDDD Z
POST-READ incre-
ment address
1...1 00 10 PPPPP EEEEE Z0 DDDDDDDDDDDDDDDD Z
The following abbreviations are used in the tables:
●
PRE = preamble, consisting of 32 logic "one" bits ("1...1")
●
PRE = preamble, consisting of 32 logic "one" bits ("1...1")
●
ST = start of frame code (2 bits), "01" for Clause 22, "00" for Clause 45, "0X" for
any, no other options permitted
●
OP = operation code or "OpCode" (2 bits). This is a frame type code specifying the
type of transaction.
For more details on the OpCode, see "OP" in Table 13-20, or TRIGger<m>:MDIO:
FRAMetype.
●
PHYAD = address of a physical layer entity (in Clause 22)
●
PRTAD = address of a port (in Clause 45)
●
REGAD = register address within a PHY (in Clause 22)
●
DEVAD = device address within a port (in Clause 45)
●
TA = turnaround time, a 2-bit time spacing between REGAD/DEVAD and DATA.
The turnaround provides the slave some time to answer upon a read command. TA
is hard-wired even in write commands, although it is not required there.
●
ADDRESS / DATA = address or payload data, 16 bits
●
IDLE = A single value (high-impedance state) indicating to the Physical Medium
Attachment (PMA) that there is no data to convey
MDIO (option R&S
RTE-K55)