COM20020ILJP datasheet(22/72 Pages) MICROCHIP

22 / 72 page

5Mbps ARCNET (ANSI 878.1) Controller with 2K x 8 On-Chip RAM

Datasheet

Revision 12-05-06

Page 22

SMSC COM20020I Rev D

DATASHEET

media (not on each individual node). The nPULSE1 signal, in this mode, is an open drain or push/pull

driver and is used to directly drive the media. It issues a 200nS negative pulse to transmit a logic "1". Note

that when used in the open-drain mode, the COM20020ID does not have a fail/safe input on the RXIN pin.

The nPULSE1 signal actually contains a weak pull-up resistor. This pull-up should not take the place of

the resistor required on the media for open drain mode.

Figure 5.4 - COM20020ID Network Using RS-485 Differential Transceivers

Figure 5.5 – Dipulse Waveform for Data of 1-1-0

In typical applications, the serial backplane is terminated at both ends and a bias is provided by the

external pull-up resistor.

The RXIN signal is directly connected to the cable via an internal Schmitt trigger. A negative pulse on this

input indicates a logic "1".

Lack of pulse indicates a logic "0".

For typical single-ended backplane

applications, RXIN is connected to nPULSE1 to make the serial backplane data line. A ground line (from

the coax or twisted pair) should run in parallel with the signal. For applications requiring different treatment

COM20020ID

+VCC

RBIAS

+VCC

RBIAS

75176B or

Equiv.

COM20020ID

20MHZ

CLOCK

(FOR REF.

ONLY)

nPULSE1

nPULSE2

DIPULSE

RXIN

100ns

200ns

400ns

COM20020ILJP Datasheet(PDF) 22 Page - Microchip Technology