DP83905AVQB datasheet(41/80 Pages) NSC

41 / 80 page

50 Register Descriptions (Continued)

TLF11498 – 21

FIGURE 24 DMA Register

Note

In the figure above registers are shown as 8- or 16-bits wide Although some registers are 16-bit intemal registers all registers are accessed as 8-bit

registers Thus the 16-bit Transmit Byte Count Register is broken into two 8-bit registers TBCR0 and TBCR1 Also TPSR PSTART PSTOP CURR and

BNRY only check or control the upper 8 bits of address information on the bus Thus they are shifted to positions 15–8 in the diagram above

54 DP8390 Core DMA Registers

The DMA Registers are partitioned into groups Transmit

Receive and Remote DMA Registers The Transmit regis-

ters are used to initialize the Local DMA Channel for trans-

mission of packets while the Receive Registers are used to

initialize the Local DMA Channel for packet Reception The

Page Stop Page Start Current and Boundary Registers are

used by the Buffer Management Logic to supervise the Re-

ceive Buffer Ring The Remote DMA Registers are used to

initialize the Remote DMA

Transmit DMA Registers

TRANSMIT PAGE START REGISTER (TPSR)

This register points to the assembled packet to be transmit-

ted Only the eight higher order addresses are specified

since all transmit packets are assembled on 256-byte page

boundaries The bit assignment is shown below The values

placed in bits D7 – D0 will be used to initialize the higher

order address (A8 – A15) of the Local DMA for transmission

The lower order bits (A7 – A0) are initialized to zero

Bit Assignment

765432

TPSR

A15

A14

A13

A12

A11

A10

(A7 – A0 Initialized to 0)

TRANSMIT BYTE COUNT REGISTER 01 (TBCR0 TBCR1)

These two registers indicate the length of the packet to be

transmitted in bytes The count must include the number of

bytes in the source destination length and data fields The

maximum number of transmit bytes allowed is 64 kbytes

The ATLANTIC Controller will not truncate transmissions

longer than 1500 bytes The bit assignment is shown below

765432

TBCR1

L15

L14

L13

L12

L11

L10

765432

TBCR0

Local DMA Receive Registers

PAGE START STOP REGISTERS (PSTART PSTOP)

The Page Start and Page Stop Registers program the start-

ing and stopping address of the Receive Buffer Ring Since

DP83905AVQB Datasheet(PDF) 41 Page - National Semiconductor (TI)

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