CS89712 datasheet(72/170 Pages) CIRRUS

72 / 170 page

CS89712

DS502PP2

3.2.1

Ethernet Port Register Window

This section refers to the eight 2-byte registers re-

siding in the 16-byte window at 0x2000.3000.

These registers are always immediately available.

3.2.1.1

Receive/Transmit Data Ports 0 & 1

These two ports are used when transferring trans-

mitting/receving data to/from the CS89712. Port 0

is used for 16-bit operations and Ports 0 and 1 are

for 32-bit operations (lower-order word in Port 0).

3.2.1.2

TxCMD Port

Software writes the Transmit Command (TxCMD)

to this port at the start of each transmit operation.

The Transmit Command indicates that the software

has a frame to be transmitted, as well as how that

frame should be transmitted. See Section 3.2.3,

“Ethernet Status/Control Registers” for more in-

formation.

3.2.1.3

TxLength Port

The length of the frame to be transmitted is written

here immediately after the Transmit Command is

written.

3.2.1.4

Interrupt Status Queue Port

This port contains the current value of the Interrupt

Status Queue (ISQ). For a more detailed descrip-

tion of the ISQ, see Section 2.31, “Managing Inter-

rupts & Status Queue”.

3.2.1.5

Ethernet Port Pointer

The Ethernet Port Pointer is written in order to ac-

cess any of the Ethernet port indexed registers

(which reside in the 4 Kbyte memory page). The

first 12 bits (bits 0 through B) of the pointer provide

the offset of the target register to be accessed dur-

ing the current operation. The next three bits (C, D,

and E) are read-only and will always read as 011b.

Any convenient value may be written to these bits

when writing to the Ethernet Port Pointer Port. The

last bit (Bit F) indicates whether or not the Ethernet

Port Pointer should be auto-incremented to the next

word location. Figure 22 shows the structure of the

Ethernet Port Pointer.

3.2.1.6

Ethernet Port Data Ports 0 and 1

The Ethernet Port Data Ports are used to transfer

data to and from any of the CS89712’s internal reg-

isters. Port 0 is used for 16-bit operations and Port

0 and 1 are used for 32-bit operations (lower-order

word in Port 0).

base + 000Bh

base + 000Ah

BitF: 0 =Pointer remains fixed

1 = Auto-Increments to next word location

Figure 22. Ethernet Port Pointer

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