[avr-chat] ATmega644 : dual USART... or not dual usart.. that, is the question !

[Vincent Trouilliez]

Hi list,

That is the question, indeed !

My AVR project currently is based on a mega32 (selected 3+ years
ago), which has a single USART. I actually need two serial links, but
since they are mutually exclusive (when I work on one, I don't need to
work on the other), it could be possible to reconfigure the USART every
time, and add some extra external circuitry to switch the Rx/Tx pins
from one serial link to the other.
But I discovered recently on AVRfreaks, that there is a cool
mega324 variant which is basically a mega32 with a second USART.
So this 324 would make my life much easier !
At the same time I am about to switch my project from a text LCD
module, to a graphical one, which means increased RAM and code
memory requirements, so I was logically eyeing the 644 instead of the
324.

Problem: I am seeing conflicting information about the 644.
On AVRfreaks, the datasheet they give, which is specific to the 644,
says that unlike the 324, and quite strangely, it does NOT have this
second USART !? :-/
OTOH, if I go on the Atmel website, they provide a unified datasheet
for the 3 variants: 164/324/644, and this paper clearly indicates that
ALL THREE variants, do have that second USART.

Since that USART is the only reason I am considering a 644, it's rather
important that I know the truth ! ;-)

I looked in the ERRATA sections of the two datasheets, and neither
mention errors regarding the available peripherals.

All I noticed is that the document # in the footer of the datasheets,
suggests that the datasheet on AVRfreaks is older (#2593) than the one
on the Atmel website (#8011).

Still, lacking any errata, I can only consider the two datasheets as
valid. So that can only mean that the 644 started it's life with one
USART, and got one later on, probably to make it consistent with the
other variants in the same series, 164 and 324.
So, how do I know if the 644 I will order, will come with one or two
USARTs, grrr...

If someone knows the story about the 644 and could shed some light, I am
all ears ! ;-)


Regards,

--
Vince, confused to say the least...