PX41CX

[goosnarrggh]

(11-02-2022 05:18 AM)Sylvain Cote Wrote:  4) you also have three USART that can be used for RS232 transmission

There aren't enough free pins to add an practical general-purpose bidirectional communication port to the current ATmega328 based design. Interaction with the outside world is only available via the 6-pin programming interface while the micro is being held in reset so the alternate functions of some of those pins are rendered inactive.

Since the AVR128D28 part has the same pin count, and all the rest of the hardware (keyboard, LCD) is also the same, very similar limitations would also apply.

Workarounds would include moving up to a part with a higher pin count, or adding I/O expander chips. But the PDIP variant of this new chip is only available in a maximum of 28 pins; moving up to a higher pin count would mean moving to surface mount would be a DIY killer. I guess adding an I/O expander might be viable. But it would also add to the complexity of what is, right now, admirable for its simplicity.