[comport] spits values one by one (actually bytes, so if a value is greater than one byte, it will be split, depending on the way you'll print it from the Arduino - Serial.print or Serial.write). you'll have to assemble them into a list (check help patch of [list] to see how to make a growing list), or make a counter and bang it on every output of [comport], pack the [comport] value with the counter value prepended and use [route].

I've made some abstractions to facilitate the communication between the Arduino and Pd, they'll might work for you. There're here https://github.com/alexdrymonitis/Arduino_Pd

The [serial_print] abstraction can use the comma as a value delimiter (if you're on Pd-extended, use [serial_print_extended] instead).