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If additional devices are connected to the ISP lines, the programmer must be
protected from any device, other than the AVR, that may try to drive the lines. This is
especially important with the SPI bus, as it is similar to the ISP interface. Applying
series resistors on the SPI lines, as depicted in Figure 4-2, is the easiest way to
achieve this.
Note that the AVR will never drive the SPI lines in a programming situation, since the
AVR is held in RESET to enter programming mode – and RESET’ing the AVR tri-
提示isp上有spi设备时应在spi线上串接电阻，接多少没有提
states all pins. |
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