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Dragon Rider 500

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General Use of the Dragon Rider 500

This page describes the features of the Dragon Rider that are not specific to a target microcontroller.  For information about using the Dragon Rider with each of the supported devices, follow the links in the navigation bar at the left.  Also, refer to the downloadable User's Guide.

Mounting the AVR Dragon

The Dragon Rider mounts on the AVR Dragon in a straightforward and obvious way.  The power, JTAG, ISP and HV_PROG headers of the Dragon all mate with header sockets on the underside of the Dragon Rider.  Pillars support the Dragon Rider and bumpon feet support the Dragon so that the headers and sockets are properly engaged but forces on both Dragon and Rider are carried to the bench.  The USB connector of the Dragon will probably touch the underside of the Dragon Rider, but this is safe and has been allowed for in the design.  The "status" LED of the Dragon is visible from the top of the assembly via a light pipe.  The second LED, which only indicates USB traffic, will not be easily visible.

Orientation and Pin 1

The normal orientation of the Dragon Rider is with the AVR Dragon's USB connector to the left and the four GPIO Port headers closest to the user.  Terms such as "upper", "left", etc. are with reference to this orientation.  All target device sockets have pin 1 at the upper-left.  All ten-pin headers (2 rows by 5 pins) have pin 1 at the lower-left.  All single-row headers have pin 1 either at the top, if they are vertically oriented, or at the left, if they are horizontally oriented.  It is generally enough to remember that pin 1 is towards the left or, if that makes no sense, at the top.

Power Sources

The target microcontroller on the Dragon Rider can generally be powered from the AVR Dragon, either directly or via a sub-regulator (see below), or from an external source.  However, when using High-Voltage Programming, the target must be powered directly from the AVR Dragon.  To power the target directly from the AVR Dragon, close SW2, which is near the bottom of the 28-pin target socket U4.

A footprint is available on the Dragon Rider for a sub-regulator between the Dragon and the target.  To use this, assemble an LM1117-family or compatible TO-220 regulator as U6, near the bottom of U3.  For example, an LM1117-3.3 will power the target with 3.3 volts, rather than approximately 5 volts from the USB port of the AVR Dragon.  As the regulator pins are spaced at 0.1 in., you could devise a plug-in arrangement for sub-regulation, but it may be a little flimsy and will need careful handling to avoid disconnecting power during important demonstrations.  The recommended position for the sub-regulator, if you use one, is underneath the Dragon Rider.  See the User's Guide for details.

If SW2 is open (OFF), targets can be powered from an external supply within the operating range of the device and of the AVR Dragon (1.8 - 5.5 V).  An auxiliary power supply can be installed on the Dragon Rider and a parts kit is available (more ...).  Be sure that the output voltage is set no higher than 5.5 V when turning this on!

Reset and Crystal/Clock Pins

The 28-, 20- and 8-pin target devices supported by the Dragon Rider share pins between the RESET, XT1 and XT2 functions and general-purpose IO ports.  Unlike the STK500, which hard-wires these pins to RESET, XT1 and XT2, the Dragon Rider allows you to configure each pin separately via a three-pin jumper.

U2 - Pins 1, 2 and 3 of the 8-pin target socket U2 connect to J8, J9 and J10, respectively.  To connect these pins to general-purpose IO ports PB5, PB3 and PB4, place shunts on pins 1 and 2 of the appropriate header.  To connect these pins to RESET, XT1 and XT2, place the shunt on pins 2 and 3.

U3 - Pins 1, 5 and 4 of the 20-pin target socket U3 connect to J7, J5 and J6, respectively.  To connect these pins to general-purpose IO ports PA2, PA0 and PA1, place shunts on pins 2 and 3 of the appropriate header.  To connect these pins to RESET, XT1 and XT2, place the shunt on pins 1 and 2.

U4 - Pins 1, 9 and 10 of the 28-pin target socket U4 connect to J13, J12 and J11, respectively.  To connect these pins to general-purpose IO ports PC6, PB6 and PB7, place shunts on pins 2 and 3 of the appropriate header.  To connect these pins to RESET, XT1 and XT2, place the shunt on pins 1 and 2.

Reset Button

For your convenience, the Dragon Rider provides a reset button.  Because the reset input to the target is used in various ways by the AVR Dragon in all its programming and debugging modes (with the possible exception of JTAG), you should not press the reset button while the AVR Dragon is working.  This will not damage anything (the Dragon Rider has been designed with this in mind), but it may disrupt whatever the Dragon is trying to do.  The reset circuit consists of a 33 kohm pullup resistor (R2) shorted to ground by the switch (SW1), with an optional de-glitch capacitor (C1) to ground and a 1 kohm current-limit resistor (R1) between the switch and the reset line to prevent damage (in case the switch is pressed when the AVR Dragon is driving the line).  The de-glitch capacitor has been found not to be necessary.

Analog Supply and Precision Reference

Two of the Dragon Rider target sockets, U1 and U4, are supplied with analog power connections and analog reference voltages.  These are necessary for the on-board analog-to-digital converters.  (The other sockets, U2 and U3, are for targets that do not have A-to-D converters.)  R4 (nominally 100 ohms) connects the AVCC pins of the targets to the normal power source.  This resistor, in conjunction with decoupling capacitor C5, reduces noise on the analog supply line.  Target microcontrollers for these sockets have an internal reference, in some cases 2.56 volts and in others 1.1 volts, and can also use the supply, VCC, as a reference, but for greatest accuracy they can be programmed to use an external reference.  The Dragon Rider connects this AREF pin to VCC via R3 (nominally 1 kohm) and to ground via the decoupling capacitor C8.  Assemble an LM431-style shunt precision reference as U5, near the top of socket U4.  This will establish an accurate analog reference voltage.  You may need to adjust the value of R3 to set an appropriate current, depending on your choice of supply and reference voltages, but the nominal 1 kohm will serve in most cases.

General-Purpose IO Ports

The four ten-pin headers at the front of the Dragon Rider connect to the GPIO ports of the target microcontroller.  In order, from left to right, they are PORT A, PORT D, PORT B and PORT C, which is the same order in which they appear on the Atmel STK500.  Connections to these headers are exactly the same as the STK500, so anything you can hook up to the STK500 you can hook up to the same port on the Dragon Rider.  Of course, not all target microcontrollers have all ports nor all eight bits of the ports they do have.  Consult the data sheet for details.  The ATmega16/32 family does, however, implement all eight bits of all four ports.