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Is it possible to re-program a soldered attiny167 on a pcb, by using isp, when one of the pins needed (MISO) has a 10K resistor pulled to ground, and the RESET pin is pulled HIGH with a 10K resistor to Vcc?

I’m using a USBasp programmer through arduino IDE.

Two others pins needed on ISP (MOSI AND SCK) are not used in the circuit and are left floating.

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2 Answers 2

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Seeing original USBAsp schematic, it's RESET are wired through 270 Ohms resistor in series and MISO are driven directly from the pin. So later should be driven just fine and RESET line will form a voltage divider across your 10K pull-up and 270 series resistor. Which will give you a 270/(270+10000) ~ 0.026 Vcc (~0.13 V if Vcc are at 5V) on the RESET pin when USBAsp will pull RESET to a ground. This is low enough for the MCU logic to recognize this at LOW logical level. So yes, that should work to enter programming mode and successfully program your MCU in-circuit.

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According to the datasheet, yes, it should be possible if set up correctly:

21.8 Serial Downloading

Both the Flash and EEPROM memory arrays can be programmed using the serial SPI bus while RESET is pulled to GND. The serial interface consists of pins SCK, MOSI (input) and MISO (output). After RESET is set low, the Programming Enable instruction needs to be executed first before program/erase operations can be executed.

(emphasis mine)

You will need to pull RESET low by connecting to ground. The USBasp should automatically accomplish this (see NStorm's answer).

I'm not sure if the arduino IDE performs memory verification using read instructions during the programming process or not, but regardless, MISO should operate just fine as an output when pulled to ground with a 10K resistor (this is generally ideal for any pin operating as an output).

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