DP8390DV datasheet(27/56 Pages) NSC

27 / 56 page

100 Internal Registers (Continued)

104 DMA REGISTERS

DMA Registers

TLF8582 – 61

The DMA Registers are partitioned into three groups Trans-

mit Receive and Remote DMA Registers The Transmit reg-

isters 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

Note

In the figure above registers are shown as 8 or 16 bits wide Although

some registers are 16-bit internal 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 posi-

tions 15-8 in the diagram above

105 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

76543210

TPSR A15

A14

A13

A12

A11

A10

(A7 – A0 Initialized to zero)

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 64k bytes

The NIC will not truncate transmissions longer than 1500

bytes The bit assignment is shown below

76543210

TBCR1 L15

L14

L13

L12

L11

L10

76543210

TBCR0

106 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

the NIC uses fixed 256-byte buffers aligned on page bound-

aries only the upper eight bits of the start and stop address

are specified

PSTARTPSTOP bit assignment

PSTART

76543210

PSTOP

A15

A14

A13

A12

A11

A10

BOUNDARY (BNRY) REGISTER

This register is used to prevent overflow of the Receive

Buffer Ring Buffer management compares the contents of

this register to the next buffer address when linking buffers

together If the contents of this register match the next buff-

er address the Local DMA operation is aborted

76543210

BNRY A15

A14

A13

A12

A11

A10

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