DP83907 datasheet(39/70 Pages) NSC

39 / 70 page

50 Register Descriptions (Continued)

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 DP83907 uses fixed 256-byte buffers aligned on page

boundaries only the upper eight bits of the start and stop

address are specified

PSTART PSTOP bit assignment

765432

PSTART

A15

A14

A13

A12

A11

A10

PSTOP

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

765432

BNRY

A15

A14

A13

A12

A11

A10

CURRENT PAGE REGISTER (CURR)

This register is used internally by the Buffer Management

Logic as a backup register for reception CURR contains the

address of the first buffer to be used for a packet reception

and is used to restore DMA pointers in the event of receive

errors This register is initialized to the same value as

PSTART and should not be written to again unless the con-

troller is Reset

765432

CURR

A15

A14

A13

A12

A11

A10

CURRENT LOCAL DMA REGISTER 01 (CLDA01)

These two registers can be accessed to determine the cur-

rent Local DMA Address

765432

CLDA1

A15

A14

A13

A12

A11

A10

765432

CLDA0

Remote DMA Registers

REMOTE START ADDRESS REGISTERS (RSAR01)

Remote DMA operations are programmed via the Remote

Start

Address

(RSAR01)

and

Remote

Byte

Count

(RBCR01) registers The Remote Start Address is used to

point to the start of the block of data to be transferred and

the Remote Byte Count is used to indicate the length of the

block (in bytes)

765432

RSAR1

A15

A14

A13

A12

A11

A10

765432

RSAR0

REMOTE BYTE COUNT REGISTERS (RCB01)

765432

RBCR1

A15

A14

A13

A12

A11

A10

765432

RBCR0

Note

RSAR0 programs the start address bits A0–A7

RSAR1 programs the start address bits A8–A15

Address incremented by two for word transfers and by one for byte trans-

fers Byte count decremented by two for word transfers and by one for byte

transfers

RBCR0 programs LSB byte count

RBCR1 programs MSB byte count

CURRENT REMOTE DMA ADDRESS (CRDA0 CRDA1)

The Current Remote DMA Registers contain the current ad-

dress of the Remote DMA The bit assignment is shown

below

765432

CRDA1

A15

A14

A13

A12

A11

A10

765432

CRDA0

Physical Address Registers (PAR0 – PAR5)

The physical address registers are used to compare the

destination address of incoming packets for rejecting or ac-

cepting packets Comparisons are performed on a byte-

wide basis The bit assignment shown below relates the se-

quence in PAR0 – PAR5 to the bit sequence of the received

packet

PAR0

DA7

DA6

DA5

DA4

DA3

DA2

DA1

DA0

PAR1

DA15

DA14

DA13

DA12

DA11

DA10

DA9

DA8

PAR2

DA23

DA22

DA21

DA20

DA19

DA18

DA17

DA16

PAR3

DA31

DA30

DA29

DA28

DA27

DA26

DA25

DA24

PAR4

DA39

DA38

DA37

DA36

DA35

DA34

DA33

DA32

PAR5

DA47

DA46

DA45

DA44

DA43

DA42

DA41

DA40

Destination Address

Source

P S

DA0

DA1

DA2

DA3

DA46

DA47

SA0

Note

PS e Preamble Synch

DA0 e PhysicalMuftcast Bit

Multicast Address Registers (MAR0 – MAR7)

The multicast address registers provide filtering of multicast

addresses hashed by the CRC logic All destination ad-

dresses are fed through the CRC logic and as the last bit of

the destination address enters the CRC the 6 most signifi-

cant bits of the CRC generator are latched These 6 bits are

then decoded bya1of64 decode to index a unique filter bit

(FB0 – 63) in the multicast address registers If the filter bit

selected is set the multicast packet is accepted The sys-

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