Hacking the Uno!

Need more memory? Need another Serial port?
Hack your Uno - add an ATMege644PA & MAX3232 (RS232 driver) for that hardware expansion that's been holding you back!

Cool, just a minor detail, the ATmega644 does not have two serial ports, the ATmega644P does, do NOT forget that "P" at the end when you are placing an order.

Per Atmel:

The high-performance, low-power Atmel 8-bit AVR RISC-based microcontroller combines 64KB ISP flash memory with read-while-write capabilities, 2KB EEPROM, 4KB SRAM, 32 general purpose I/O lines, 32 general purpose working registers, real time counter, three flexible timer/counters with compare modes and PWM,


byte oriented 2-wire serial interface, 8-channel/10-bit A/D converter with optional differential input stage with programmable gain, programmable watchdog timer with internal oscillator, SPI serial port, JTAG (IEEE 1149.1 compliant) test interface for on-chip debugging, and six software selectable power saving modes. The device operates between 2.7-5.5 volts.


ATmega644P (Mature product; not recommended for new designs. Replaced by ATmega644PA.)

So why do you say one part type has 1 USART and the other has 2?

Per Atmel, but probably updated by some intern who used CTRL-C CTRL-V too much

because, see attached

I've updated the original post to reflect that. Thanks.

I suggest a bit of suspicion when it comes to the 644 datasheet. In the old forum there was a discussion about the number of timers on the 644. Assuming I remember correctly, the conclusion was that the information in the datasheet was wrong and that Atmel knew of the problem.

Well, the 644 version sold as the Sanguino definitely has 2 serial ports. I don't about the timers, have not done any playing with those.


Any one know how to mod the UNO into having all the digital pins as PWM and not just the few that are already set.

Any help would be appreciated.