To allow programming of targets running at any

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Unformatted text preview: trol line (Reset). To allow programming of targets running at any allowed voltage (2.7 - 6.0 V), the programmer can draw power from the target system (VCC). This eliminate the need for a separate power supply for the programmer. Alternatively, the target system can be supplied from the programmer at programming time, eliminating the need to power the target system through its regular power connector for the duration of the programming cycle. Figure 2 shows the connector used by this In-System Programmer to connect to the target system. The standard connector supplied is a 2 x 3 pin header contact, with pin spacing of 100 mils. Figure 2. Recommended In-System Programming Interface Connector Layout (Top View) MISO SCK RESET 1 2 3 4 5 6 VCC MOSI GND Hardware Design Considerations To allow In-System Programming of the AVR microcontroller, the In-System Programmer must be able to override the pin functionality during programming. This section describes the details of each pin used for the programming operation. GND The In-System Programmer and target system need to operate with the same reference voltage. This is done by connecting ground of the target to ground of the programmer. No special considerations apply to this pin. RESET The target AVR microcontroller will enter Serial Programming mode only when its reset line is active (low). When erasing the chip, the reset line has to be toggled to end the erase cycle. To simplify this operation, it is recommended that the target reset can be controlled by the In-System Programmer. Immediately after Reset has gone active, the In-System Programmer will start to communicate on the three dedicated SPI wires SCK, MISO, and MOSI. To avoid driver contention, a series resistor should be placed on each of the three dedicated lines if there is a possibility that external circuitry could be driving these lines. The connection is shown in Figure 3. The value of the resistors should be chosen depending on the circuitry connected to the SPI bus. Note that the 2 AVR910 0943E–AVR–08/08 AVR910 AVR microcontroller will automatically set all its I/O pins to inputs, with pull ups disabled, when Reset is active. Table 1. Connections Required for In-System Programming Pin Name Comment SCK Serial Clock Programming clock, generated by the In-System Programmer (Master) MOSI Master Out – Slave In Communication line from In-System Programmer (Master) to target AVR being programmed (Slave) MISO Master In – Slave Out Communication line from target AVR (Slave) to InSystem Programmer (Master) GND Common Ground The two systems must share the same common ground RESET Target AVR MCU Reset To enable In-System Programming, the target AVR Reset must be kept active. To simplify this, the In-System Programmer should control the target AVR Reset VCC Target Power To allow simple programming of targets operating at any voltage, the In-System Programmer can draw power from the target. Altern...
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This note was uploaded on 02/04/2014 for the course ENGN 3213 taught by Professor Gerardborg during the Three '12 term at Australian National University.

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