Datasheet

78Q2120C

10/100BASE-TX

Transceiver

The 78Q2120C implements 11 16-bit registers, which are accessible via the MDIO and MDC pins. The supported

registers are shown below in the following table. Attempts to read unsupported registers will be ignored and the

MDIO pin will not be enabled as an output, as per the IEEE 802.3 specification. All of the registers except those

which are unique to the 78Q2120C, will respond to the broadcast PHYAD value of ‘00000’. The registers specific

to the 78Q2120C occupy address space MR16-22.

ADDRESS SYMBOL NAME DEFAULT (HEX)

0 MR0 Control (3100)

1 MR1 Status (7809)

2 MR2 PHY Identifier 1 000E

3 MR3 PHY Identifier 2 70C9

4 MR4 Auto-Negotiation Advertisement (01E1)

5 MR5 Auto-Negotiation Link Partner Ability 0000

6 MR6 Auto-Negotiation Expansion 0000

7 MR7 Not Implemented 0000

8-14 MR8-14 Reserved 0000

15 MR15 Not Implemented 0000

16 MR16 Vendor Specific (0140)

17 MR17 Interrupt Control/Status Register 0000

18 MR18 Diagnostic Register 0000

19 MR19 Transceiver Control 4XXX

20-22 MR20-MR22 Reserved 0000

Legend:

TYPE DESCRIPTION TYPE DESCRIPTION

R Readable by management. W Writeable by management.

SC Writeable by management. Self

Clearing.

RC Readable by management.

Cleared upon a read operation.

0/1 Default value upon power up or

reset.

(0/1) Default value dependent on pin

settings. The value in bracket

indicates typical case.