Re: petSD project page

From: Ethan Dicks <>
Date: Wed, 8 Jun 2011 21:18:58 -0500
Message-ID: <>
On Wed, Jun 8, 2011 at 8:04 PM, Nils Eilers <> wrote:
>> I happen to have a couple of each of these lying about...
>> They were designed with the ATmega644P in mind...
> At the moment, it takes 52 KB and would fit into a 644p. RAM isn't a problem as well though you will have less buffers available.

The 644P has 4 KB of on-board RAM, the 1284P has 16 KB, so I can see
how buffer management could be an issue.

> But since there are still some features missing and there's not too much free space, I don't recommend the 644p for this design.
> If you used a socket for the 644p (I guess you did), you can replace the 644p at any time later by a pin compatible 1284p so
> there's no problem at all.

The Sanguino has a 40-pin socketed DIP, and the Makerbot Motherboard
has a 44-pin TQFP (SMT) 644P.  I don't have the opportunity to drop a
1284P on the Makerbot Motherboard (without removing a working 644P),
so it makes the idea less feasible if it *must* use a 1284P.

On the bright side, the Sanguinos I have are sitting idle, so perhaps
it's worth picking up something like this:

... to talk to an SD card, or this:

... to get an SD socket *and* an RTC in one place.

(the Sanguino doesn't use the Arduino shield specification, but enough
of the right signals are all there - it just takes a custom wiring job
- I could possibly do it on an Arduino prototyping shield ( ) - I have those handy, too).

>> ...  I am curious if it would be worth attempting to make a small riser board
>> with the SN75160/75161 on it
> Go for it! :-)
> I'll build the firmware if you've done your hardware. Takes about one hour only.
> Do you think, you can create the schematic by yourself or should I made one for you?

I understand the IEEE end of the SN75160/75161 just fine (I've owned
PETs and C-64s a long time).  I would just need to know what ports
were preferred or not preferred (I did see the general notes on the
petSD page about grouping of signals)

I'm fine with building my own firmware from source - I do it all the
time for Arduino (and have been doing it since the early days of the

>> and possibly adding support to the code to use a DS1307
> I already read a datasheet of this nice RTC back then but I couldn't use it in the early AVR at 3.3V days... ;-/


> But now the AVR runs at 5V, so I'll get some and add support for them. It needs less external parts, that's great.

It's an easy chip to use - you can either grab the "Wire" library, or
it's not too bad to bang out the I2C stuff standalone if space is an

I'm building an ATmega328-based LED clock (60 LEDs for
seconds/minutes, 12 LEDs for hours) - it has a DS1307 and uses the
Wire library and the Time library and the code (including reading
buttons and setting the time) fits in under 6K.

> Do you have a JTAG interface?

There is an ICSP port on one end (2x3 2.54mm pins).  I have a $20
USBtinyISP for programming via the ICSP, or if there's room for an
Arduino boot loader (2K), one can upload application code via the
serial pins (both using AVRdude, but with different parameters).

> Is there a serial interface for reading debug output? I didn't see a RS-232 voltage converter or serial-USB-adapter on that board.

There is neither on that board.  The 1x6 2.54mm connector on one end
is one of the standard Arduino serial interfaces (Vcc, GND, TxD, RxD
and a reset line that follows one of the serial hardware handshake
lines).  I have a couple of $3 external 7404-based RS-232 converters
and a $20 USB-TTL cable that's standard with Makerbots.  The Sanguino
is one of the Arduino designs that doesn't include the serial hardware
with every board to keep costs down.  $30 Arduinos include the serial
hardware.  $10 Arduinos do not.

Thanks for your answers - based on them, it sounds feasible to noodle
around for now with a Motherboard and an external DS1307 board (I
already have that) and to just build the IEEE level shifter on a small
bit of stripboard.  I just see it as a block-level-compatible
prototype that could let me use stuff I already have lying about.

If I can get a couple of SN75160/75161 level shifters on my next parts
order, I may throw one of these together (later this summer).



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Received on 2011-06-09 03:00:12

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