DP83266 datasheet(116/152 Pages) NSC

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70 Control Information (Continued)

System Interface Compare Register (SICMP)

The System Interface Compare Register (SICMP) is used in comparison with a write access of a conditional write register The

System Interface Compare Register is loaded on a read of any of the system interface conditional event Attention Registers or

by directly writing to it

This register is not altered upon reset

Access Rules

Address

Read

Write

11Fh

Always

CMP7

CMP6

CMP5

CMP4

CMP3

CMP2

CMP1

CMP0

Bit

Symbol

Description

D7 – D0

CMP7 – CMP0

Compare

These bits are compared to bits D7 – D0 of the accessed System Interface register Only

the bits in the System Interface Attention Register that have the same current value as the

corresponding bit in the Compare register will be updated with the new value

78 POINTER RAM REGISTERS

Pointer RAM Registers contain pointers to all data and De-

scriptors manipulated by the MACSI device namely Input

and Output Data Units Input and Output Data Unit Descrip-

tors Request Descriptors Confirmation Messages and

Pool Space Descriptors Pointer RAM Registers are shown

Figure 7-3

79 LIMIT RAM REGISTERS

The Limit RAM Registers are used by both the Indicate and

Request machines Limit RAM Registers contain data val-

ues that define how far the MACSI device may advance in

each of its ten queues The Limit RAM Registers do not

define the wrap point for each queue which is fixed at either

1 kByte or 4 kBytes Limit RAM Registers are shown in

Fig-

ure 7-4

710 DESCRIPTORS

Descriptors are used to observe and control the operation

of the MACSI device They contain address status and

control information about Indicate and Request operations

Descriptors are stored in lists and wrap-around queues in

memory external to the MACSI device and accessed by the

MACSI device via the ABus Descriptors include the follow-

ing Input Data Unit Descriptors (IDUDs) specify the loca-

tion size part and status information for Input Data Units

Output Data Unit Descriptors (ODUDs) specify the location

and size of Output Data Units For multi-ODUD frames they

also specify which part of the frame is pointed to by the

ODUD Pool Space Descriptors (PSPs) describe the loca-

tion and size of a region of memory space available for writ-

ing Indicate data Request Descriptors (REQs) describe the

location of a stream of Output Data Unit Descriptors and

contain operational parameters Confirmation Status Mes-

sages (CNFs) describe the result of a Request operation

711 OPERATING RULES

Multi-Byte Register Ordering

When referring to multi-byte fields byte 0 is always the most

significant byte When referring to bits within a byte bit 7 is

the most significant bit and bit 0 is the least significant bit

When referring to the contents of a byte the most signifi-

cant bit is always referred to first

116

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