COM20020IP3V datasheet(18/82 Pages) SMSC

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The above sampling and delaying signals are

supplied to the Read Pulse Generation logic

which generates the clearing pulse for the

Diagnostic register and generates the starting

pulse of the RAM Arbitration. Typical delay time

between nRD and nRD1 is around 15nS and

between nRD1 and nRD2 is around 10nS.

Longer pulse widths are needed due to these

delays on nRD signal. However, the CPU can

insert some wait cycles to extend the width

without any impact on performance.

The RBUSTMG bit was added to Disable/Enable

the High Speed CPU Read function. It is defined

as:

RBUSTMG=0,

Disabled

(Default);

RBUSTMG=1, Enabled.

In the MOTOROLA CPU mode (DIR, nDS

mode), the same modifications apply.

RBUSTMG BIT

BUS TIMING MODE

Normal Speed CPU Read and Write

High Speed CPU Read and Normal Speed CPU Write

TRANSMISSION MEDIA INTERFACE

The bottom halves of Figures 2 and 3 illustrate the

COM20020 interface to the transmission media

used to connect the node to the network. Table 1

lists different types of cable which are suitable for

ARCNET applications.

1 The user may interface to

the cable of choice in one of three ways:

Traditional Hybrid Interface

The Traditional Hybrid Interface is that which is

used with previous ARCNET devices. The Hybrid

Interface is recommended if the node is to be

placed in a network with other Hybrid-Interfaced

nodes. The Traditional Hybrid Interface is for use

with nodes operating at 2.5 Mbps only.

The

transformer coupling of the Hybrid offers isolation

for the safety of the system and offers high

Common Mode Rejection. The Traditional Hybrid

Interface uses circuits like SMSC's HYC9068 or

HYC9088 to transfer the pulse-encoded data

between the cable and the COM20020.

The

COM20020 transmits a logic "1" by generating two

100nS

non-overlapping

negative

pulses,

nPULSE1 and nPULSE2.

Lack of

pulses

indicates a logic "0". The nPULSE1 and nPULSE2

signals are sent to the Hybrid, which creates a

200nS dipulse signal on the media.

COM20020IP3V 数据表(PDF) 18 Page - SMSC Corporation

COM20020IP3V 数据表(HTML) 18 Page - SMSC Corporation

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