COM20022ITQFP datasheet(44/83 Pages) SMSC

44 / 83 page

10 Mbps ARCNET (ANSI 878.1) Controller with 2Kx8 On-Board RAM

Datasheet

Rev. 08-18-03

Page 44

SMSC COM20022I

DATASHEET

Table 6.10 - Setup 1 Register

BIT

BIT NAME

SYMBOL

DESCRIPTION

Pulse1 Mode

P1MODE

This bit determines the type of PULSE1 output driver used in

Backplane Mode. When high, a push/pull output is used. When

low, an open drain output is used. The default is open drain.

Four NACKS

FOUR

NACKS

This bit, when set, will cause the EXNACK bit in the Diagnostic

Status Register to set after four NACKs to Free Buffer Enquiry are

detected by the COM20022I. This bit, when reset, will set the

EXNACK bit after 128 NACKs to Free Buffer Enquiry. The default

is 128.

Reserved

Do not set.

Receive All

RCVALL

This bit, when set, allows the COM20022I to receive all valid data

packets on the network, regardless of their destination ID. This

mode can be used to implement a network monitor with the

transmitter on- or off-line. Note that ACKs are only sent for

packets received with a destination ID equal to the COM20022I's

programmed node ID. This feature can be used to put the

COM20022I in a 'listen-only' mode, where the transmitter is

disabled and the COM20022I is not passing tokens. Defaults low.

3,2,1

Clock Prescaler Bits

3,2,1

CKP3,2,1

These bits are used to determine the data rate of the COM20022I.

The following table is for a 20 MHz crystal: (Clock Multiplier is

bypassed)

CKP3

CKP2

CKP1

DIVISOR

128

SPEED

2.5Mbs

1.25Mbs

625Kbs

312.5Kbs

156.25Kbs

Note:

The lowest data rate achievable by the COM20022I is

156.25Kbs. Defaults to 000 or 2.5Mbs. For Clock Multiplier

output clock speed greater than 20 MHz, CKP3, CKP2 and

CKP1 must all be zero.

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.

Note:

For clock multiplier output clock speeds greater than 40

MHz, SLOWARB must be set. Defaults to low.

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