AN10658_1

© NXP B.V. 2008. All rights reserved.

Application note

Rev. 01 — 26 February 2008

8 of 28

NXP Semiconductors

AN10658

The other end of the cable is fitted into the RJ45 jack CON2 of a second or ‘remote’

P82B96/PCA9600 daughter board. This ‘remote’ board will derive its 5 V supply from

the first board, via the cable and CON2. Use of CON2, with its different wiring

configuration, provides the necessary crossover linking from Tx on one board to Rx

on the other.

Ensure that the 5 V power selection jumper is fitted between pins 2 and 3 on header

J1 or that some alternative logic supply voltage is connected to pin 2 on J1 so that

for probing on the 8-pin header J2. They are also available on the 9-pin header CON4

in the same format as on the I2C2005-1 expansion header.

Note that only the ‘switched 5 V’ supply from the I2C2005-1 board is used on

CON1/CON2. The un-switched 5 V and 3.3 V supplies are not available on the Cat5e

cable and therefore are not available on CON4 in modes where boards are linked only

by the Cat5e cable.

See Section 3.2 for further details of this application.

3.1 Generating Fm+ compatible signals at CON1

This operating mode is intended for providing Fm+ drive signals to enable testing of ICs or

modules that require up to 30 mA driver sink capability to allow low resistance pull-ups to

be used to achieve fast rise times.

The pull-up resistor actually fitted on the P82B96/PCA9600 demonstration board is

1.15 k

Ω, being the series combinations of R5 + R6 and R9 + R10.

Provision is made for fitting either leaded or chip resistors in parallel with this pull-up to

achieve whatever resultant value is desired. Those resistors may be fitted as R4,5,8,9.

Note that to meet the 120 ns Fm+ rise time requirement the maximum capacitance load

allowed with the fitted 1.15 k

Ω pull-up is only 120 pF. The typical blue Cat5e

communication cable is about 46 pF/m so connection cables must be kept short.

It is recommended not to attempt driving long cables with this pull-up value; the 4-signal

mode is much more reliable and allows higher speed.

An example of using the board in this Fm+ mode would be to directly drive the FDI

PCA9633 LED driver demonstration board’s Fm+ bus using a short communications cable

between CON1 and either RJ45 jack on the FDI board. The settings on the boards should

be:

– Switches 1 and 2 closed (on) [Selects Fm+ mode]

– Switches 3 and 4 open (off) [Selects Fm+ mode]

– Switches 1-3 set as advised in the 2005-1 user guide [address selection]. The

address used with Win USB Lite requires Switch 1 = ON, Sw 2 = OFF, Sw 3 = ON.

– Switch 4 ON. [The cable core 6 is used as a ground and this sets OE low = active.]