Atmel AT91EB40A, Руководство пользователя

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4-2 AT91EB40A Evaluation Board User Guide
2635C–ATARM–13-May-05
same time (i.e., one as a boot memory and the other as data storage memory). In fact,
the AT91 NCS0 chip select line is connected to U1A or U1B chip select line according to
the position of CB11. See “Appendix A – Configuration Straps” and Figure 6-8 in
“Appendix B – Schematics” .
4.4 Power and
Crystal Quartz
The system clock is derived from a single 66 MHz crystal oscillator. An external clock
can be input on the EB40A via the EBI connector on pin B4 - EBI_MCKI. See Figure 6-6
in “Appendix B – Schematics” .
The voltage regulator U9 provides 3.3V to VDDIO and to all other devices of the board.
The voltage regulator U11 provides 1.8V for VDDCORE of the AT91R40008.
Power can be applied via the 2.1mm connector to the regulator in either polarity
because of the diode-rectifying circuit.
4.5 Push-buttons,
LEDs and Serial
Interfaces
4.5.1 Push-buttons and
LEDs Figure 6-3 in “Appendix B – Schematics” shows push buttons and LEDs. SW1, SW2,
SW3 and SW4 push buttons are debounced, buffered and connected to P12/FIQ,
P9/IRQ0, P1/TIOA0 and P2/TIOB0, respectively. The eight general-purpose LEDs are
connected to PIO (P15 to P19 and P3 to P6).
4.5.2 Serial Interface Two 9-way D-type connectors (P3/P4) 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 is DCD, DSR and DTR.
Serial port B (P4) is a DB9 male connector with TXD and RXD in conformance with the
standard RS-232 pinout. Apart from TXD, RXD and ground, the other pins are not
connected.
A MAX3223 device (U10) and associated bulk storage capacitors provide RS-232 level
conversion.
4.6 Reset Circuit and
JTAG Interface
4.6.1 Reset Circuit A supervisory circuit has been included in the design to detect and consequently reset
the board when the 3.3V supply voltage drops below 2.7V. Note that this voltage can be
changed depending on the board production series. The supervisory circuit also pro-
vides a debounced reset signal. This device also generates the reset signal in case of
watchdog timeout, as the pin NWDOVF of the AT91R40008 is connected on its input
/MR.
The assertion of this reset signal lights the red RESET LED (D10). By pressing the
CLEAR RESET push button (S2), the LED is turned off.