DP83902A datasheet(29/70 Pages) NSC

29 / 70 page

100 Internal Registers (Continued)

103 REGISTER DESCRIPTIONS

(Continued)

DATA CONFIGURATION REGISTER (DCR)

0EH (WRITE)

This Register is used to program the ST-NIC for 8- or 16-bit memory interface select byte ordering in 16-bit applications and

establish FIFO thresholds The DCR must be initialized prior to loading the Remote Byte Count Registers LAS is set on

power up

76543210

FT1

FT0

ARM

LAS

BOS

WTS

Bit

Symbol

Description

WTS

Word Transfer Select

0 Selects byte-wide DMA transfers

1 Selects word-wide DMA transfers

WTS establishes byte or word transfers for both Remote and Local DMA transfers

Note

When word-wide mode is selected up to 32k words are addressable A0 remains low

BOS

Byte Order Select

0 MS byte placed on AD15 – AD8 and LS byte on AD7 – AD0 (32xxx 80x86)

1 MS byte placed on AD7 – AD0 and LS byte on AD15 – A8 (680x0)

Ignored when WTS is low

LAS

Long Address Select

0 Dual 16-bit DMA mode

1 Single 32-bit DMA mode

When LAS is high the contents of the Remote DMA registers RSAR0 1 are issued as A16 – A31 Power up

high

Loopback Select

0 Loopback mode selected Bits D1 and D2 of the TCR must also be programmed for Loopback operation

1 Normal Operation

ARM

Auto-Initialize Remote

0 Send Command not executed all packets removed from Buffer Ring under program control

1 Send Command executed Remote DMA auto-initialized to remove packets from Buffer Ring

Note

Send Command cannot be used with 680x0 byte processors

FT0

FIFO Threshold Select

Encoded FIFO threshold Establishes point at which bus is requested when filling or

emptying the FIFO During reception the FIFO threshold indicates the number of bytes (or words) the FIFO has

and

filled serially from the network before bus request (BREQ) is asserted

FT1

Note

FIFO threshold setting determines the DMA burst length

Receive Thresholds

FT1

FT0

Word Wide

Byte Wide

1 Word

2 Bytes

2 Words

4 Bytes

4 Words

8 Bytes

6 Words

12 Bytes

During transmission the FIFO threshold indicates the number of bytes (or words) the FIFO has filled from the

Local DMA before BREQ is asserted Thus the transmission threshold is 13 bytes minus the received

threshold

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