Help! ATMEGA1280&1281 Weird JTAG & ISP Header Pinouts

[Rjc987]

Hi guys, hopefully somebody can help me with us-I’m used to PICs, and that Mel is totally new to me, so this is even more confusing. I am working on a bioteck eon Spectrophotometer that’s giving really weird errors and I was hoping to have a look under the hood to get a feel for what’s going on. The main board and sensor board both use ATmega, the main board 1280 and 1281, and the sensor board 164p. Both have a number of connectors labeled JTAG for each system (motor control, UI control, Sensors), and additionally, the main board has a header labeled ISP. Great, right? Well, not so fast because they all have really bizarre pin outs. The JTAG connectors at least have the correct connections even though they’re in odd places, But the ISP connector only has SDA, SCL, RX, TX, ICP1(??), VCC, and ground. So it’s actually I2C and UART with an extra ICP1? I’ve included a picture of the connectors on the board and my terrible sketch of the different pin outs.  I was trying to use a USBASP But obviously that’s not going to work, so I ordered an AVR dragon, but have any of you seen this? Is this normal? And what should I do about connections?

Thanks!

[fchk]

Atmel ICE uses these connections. These connectors are the current standard for ARM Cortex A/M/R as mandated by ARM, and ATmel has used them for both the ARM as well as the Atmel connector on the Atmel ICE.

https://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-ICE_UserGuide.pdf

[Rjc987]

Ahhh! Thanks! So is the Mplab snap compatible with that pinout? I really can’t justify spending $200 for the ICE just for this one project

[bingo600]

Maybe you can fix the snap

https://swharden.com/blog/2022-12-09-avr-programming/
http://ww1.microchip.com/downloads/en/DeviceDoc/ETN36_MPLAB%20Snap%20AVR%20Interface%20Modification.pdf

Snap UG
https://ww1.microchip.com/downloads/en/DeviceDoc/50002787C.pdf

/Bingo