DP83916 datasheet(39/96 Pages) NSC

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40 SONIC-16 Registers (Continued)

437 Data Configuration Register 2

(RAk50l e 3Fh)

This register

(Figure 4-10) is for enabling the extended bus interface options

A hardware reset will set all bits in this register to ‘‘0’’ except for the Extended Programmable Outputs which are unknown until

written to and bits 5 to 11 which must always be written with zeroes but are ‘‘don’t cares’’ when read A software reset will not

affect any bits in this register This register should only be written to when the SONIC-16 is in software reset (the RST bit in the

Command Register is set)

98765

EXPO3

EXPO2

EXPO1

EXPO0

0000

0PCM

PCNM

RJCM

FIGURE 4-10 Data Configuration Register 2

Field

Meaning

EXPO30 EXTENDED PROGRAMMABLE OUTPUTS

PROGRAM HOLD

PCM

PACKET COMPRESS WHEN MATCHED

PCNM

PACKET COMPRESS WHEN NOT MATCHED

RJCM

REJECT ON CAM MATCH

Bit

Description

15–12

EXPOk30l EXTENDED PROGRAMMABLE OUTPUTS

These bits program the level of the Extended User outputs (EXUSRk30l) when the SONIC-16 is a bus master

Writing a ‘‘1’’ to any of these bits programs a high level to the corresponding output Writing a ‘‘0’’ to any of these

bits programs a low level to the corresponding output EXUSRk30l are similiar to USRk10l except that

EXUSRk30l are only available when the Extended Bus mode is selected (bit 15 in the DCR is set to ‘‘1’’ see

Section 432)

11 – 5

Must be written with zeroes

PH PROGRAM HOLD

When this bit is set to ‘‘0’’ the HOLD request output is asserteddeasserted from the falling edge of bus clock If this

bit is set to ‘‘1’’ HOLD will be asserteddeasserted

clock later on the rising edge of bus clock

Must be zero

PCM PACKET COMPRESS WHEN MATCHED

When this bit is set to a ‘‘1’’ (and the PCNM bit is reset to a ‘‘0’’) the PCOMP output will be asserted if the

destination address of the packet being received matches one of the entries in the CAM (Content Addressable

Memory) This bit along with PCNM is used with the Management Bus of the DP83950 Repeater Interface

Controller (RIC) See the DP83950 datasheet for more details on the RIC Management Bus This mode is also called

the Managed Bridge Mode

Note 1

Setting PCNM and PCM to ‘‘1’’ at the same time is not allowed

Note 2

If PCNM and PCM are both ‘‘0’’ the PCOMP output will remain TRI-STATE until PCNM or PCM are changed

PCNM COMPRESS WHEN NOT MATCHED

When this bit is set to a ‘‘1’’ (and the PCM bit is set to ‘‘0’’) the PCOMP output will be asserted if the destination

address of the packet does not match one of the entries in the CAM See the PCM bit above This mode is also

called the Managed Hub Mode

Note

PCOMP will not be asserted if the destination address is a broadcast address This is true regardless of the state of the BRD bit in the

Receive Control Register

RJCM REJECT ON CAM MATCH

When this bit is set to ‘‘1’’ the SONIC-16 will reject a packet on a CAM match Setting RJCM to ‘‘0’’ causes the

SONIC-16 to operate normally by accepting packets on a CAM match Setting this mode is useful for a small bridge

with a limited number of nodes attached to it RJCM only affects the CAM though Setting RJCM will not invert the

function of the BRD PRO or AMC bits (to accept broadcast all physical or multicast packets respectively) in the

Receive Control Register (see Section 433) This means for example that it is not possible to set RJCM and BRD

to reject all broadcast packets If RJCM and BRD are set at the same time however all broadcast packets will be

accepted but any packets that have a destination address that matches an address in the CAM will be rejected

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