COM20019I-HT datasheet(33/65 Pages) SMSC

33 / 65 page

Low Cost ARCNET (ANSI 878.1) Controller with 2K x 8 On-Board RAM

SMSC COM20019I

Page 33

Rev. 03-07-06

DATASHEET

BIT

BIT NAME

SYMBOL

DESCRIPTION

3,2,1

Clock Prescaler

Bits 3,2,1

CKP3,2,1

These bits are used to determine the data rate of the

COM20019I. The following table is for a 20 MHz crystal:

CKP3

CKP2

CKP1

DIVISOR

128

SPEED

312.5 Kbs

156.25 Kbs

Note: The lowest data rate achievable by the COM20019I

is 156.25 Kbs. Defaults to 011 or 312.5 Kbps.

Slow Arbitration

Select

SLOWARB

This bit, when set, will divide the arbitration clock by 2.

Memory cycle times will increase when slow arbitration is

selected.

Defaults to low.

Table 6.11 - Setup 2 Register

BIT

BIT NAME

SYMBOL

DESCRIPTION

Read Bus Timing

Select

RBUSTMG This bit is used to Disable/Enable the High Speed CPU

Read function for High Speed CPU bus support.

RBUSTMG=0: Disable (Default), RBUSTMG=1: Enable. It

does not influence write operation. High speed CPU Read

operation is only for non-multiplexed bus.

6,5,4

Reserved

These bits are undefined.

Enhanced

Functions

This bit is used to enable the new enhanced functions in the

COM20019I. EF = 0: Disable (Default), EF = 1: Enable. If

EF = 0, the timing and function is the same as in the

COM20020, Revision B. See appendix “A”. EF bit must be

‘1’ if the data rate is over 5Mbps.

EF bit should be ‘1’ for new design customers.

EF bit should be ‘0’ for replacement customers.

No Synchronous

NOSYNC

This bit is used to enable the SYNC command during

initialization. NOSYNC= 0, Enable (Default) The line must

be idle for the RAM initialization sequence to be written.

NOSYNC= 1, Disable:) The line does not have to be idle for

the RAM initialization sequence to be written. See appendix

“A”.

1,0

Reconfiguration

Timer 1, 0

RCNTM1,

These bits are used to program the reconfiguration timer as

a function of maximum node count. These bits set the time

out period of the reconfiguration timer as shown below. The

time out periods shown are for 312.5 Kbps.

RCNTM1

RCNTM0

Time Out

Period

Max Node Count

6.72 S

Up to 255 nodes

1.68 S

Up to 64 nodes

840 mS

Up to 32 nodes

420 mS*

Up to 16 nodes

Note*: The node ID value 255 must exist in the network for

420 mS timeout to be valid.

COM20019I-HT Datasheet(PDF) 33 Page - SMSC Corporation

COM20019I-HT Datasheet(HTML) 33 Page - SMSC Corporation

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