COM20022V-HT Ver la hoja de datos (PDF) - SMSC -> Microchip

Número de pieza

componentes Descripción

Lista de partido

COM20022V-HT

10Mbps ARCNET controller with 2Kx8 on-board RAM

SMSC -> Microchip 

A2-A0, nCS

nRD

Delayed nRD

(nRD1)

VALID

Sampled A2-A0, nCS

VALID

More delayed nRD

(nRD2)

FIGURE 8 - HIGH SPEED CPU BUS TIMING - INTEL CPU MODE

The I/O address and Chip Select signals, which

are supplied to the data output logic, are not

sampled. Also, the nRD signal is not delayed,

because the above sampling and delaying paths

decrease the data access time of the read cycle.

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 BUSTMG pin is used to support this

function. It is used to Enable/Disable the High

Speed CPU Read and Write function. It is

defined as: BUSTMG = 0, the High Speed CPU

Read and Write operations are enabled;

BUSTMG = 1, the High Speed CPU Read and

Write operations are disabled if the RBUSTMG

bit is 0. If BUSTMG = 1 and RBUSTMG = 1,

High Speed CPU Read operations are enabled

(see definition of RBUSTMG bit below).

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.

BUSTMG PIN

0

1

1

RBUSTMG BIT

X

0

1

BUS TIMING MODE

High Speed CPU Read and Write

Normal Speed CPU Read and Write

High Speed CPU Read and Normal Speed CPU Write

TRANSMISSION MEDIA INTERFACE

Traditional Hybrid Interface

The bottom halves of Figures 2 and 3 illustrate the

COM20022 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:

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

23

Share Link: