I'm designing a circuit with an Atmega88, a 4 pin connector (for power supply and TWI) and an ISP interface.
Since space on the PCB is scarce I wondered if it would be OK to connect two of the ISP lines (let's say MOSI and MISO) with the connector pins that also go to SDA and SCL.
That way I could use my standard connector and just two additional wires for programming.
MISO ---> Connector Pin 1 <--- SDA MOSI ---> Connector Pin 2 <--- SCL GND ---> Connector Pin 3 VCC ---> Connector Pin 4 SCK ---> Programming Pin 1 !RST ---> Programming Pin 2
- Am I right in thinking that since I'm not using SPI at all other than for programming, those pins should be tri-stated in normal operation?
- What exactly happens to all the other pins during programming? Can I safely program the chip with MISO and MOSI connected to SDA and SCL?
Thanks in advance,