Circuit Description

AT91EB42 Evaluation Board User Guide

4-3

of watchdog time-out as the pin NWDOVF of the AT91M42800 is connected to its input

MR.

The assertion of this reset signal will light up the red RESET LED (D10). By pressing the

CLEAR RESET push button (S1), the LED can be turned off.

Another supervisory circuit initializes separately the microcontroller-embedded

JTAG/ICE interface when the 3.3V supply voltage drops below 3.0V. Note that this volt-

age can be changed, depending on the board production series. These separated reset

lines allow the user to reset the board without resetting the JTAG/ICE interface while

debugging.

The schematic (Figure 6-5 on page 6-6 in Section 6, "Appendix B - Schematics") also

shows eight general-purpose LEDs connected to port B PIO pins (PB8 to PB15).

Two 9-way D-type connectors (P3/4) are provided for serial port connection.

Serial port A (P3) is used primarily for host PC communication and is a DB9 female con-

nector. TXD and RXD are swapped so that a straight-through cable can be used. CTS

and RTS are connected together, as are DCD, DSR and DTR.

Serial port B (P4) is a DB9 male connector with TXD and RXD obeying the standard

RS-232 pinout. Apart from TXD, RXD and ground, the other pins are not connected.

LEDs are connected to the TX and RX signals of both serial ports and show activity on

these serial links.

A MAX3223 device (U10) and associated bulk storage capacitors provide RS-232 level

conversion.

4.7

Layout Drawing

The layout diagram (Figure 6-1 on page 6-2 in Section 6, “Appendix B – Schematics”)

shows an approximate floorplan for the board. This has been designed to give the low-

est board area, while still providing access to all test points, jumpers and switches on

the board.

The board is provided with four mounting holes, one at each corner, into which feet are

attached. The board has two signal layers and two power planes.