Isp schematic for atmega1281

[hobbss]

So I found out the hard way that the ATMEGA1281 does not use the SPI pins for ISP (what's that pnemonic about how to spell "assume"?).

I have a second design that I am ready to send to the board house, but would like to confirm that I actually have the ISP pins identified correctly. I am using a AVRISP mkii programmer (6 pin)

As I [now] understand it, the connections should be:

ISP Connector  ---->  ATMEGA
MISO (pin 1) -------- PDO = PE1 on 1281
MOSI (pin 4) -------- PDI = PE0 on 1281
SCK (pin 3) --------- PB1 on 1281
GND, Vcc -- GND, Vcc.

Furthermore, because I also have an RS-232 transceiver on these pins, I think I need a series resistor on those two lines, between the transceiver and where the ISP connector ties in

MAX232 --- 1kOhm resistor -----+-----PEx
                               |
                               |
                               |
                           ISP Signal

I have attached a schematic describing what I mean.

Does anyone have any experience with the ATMEGA1281 ISP pins?

 

[ckshivaram]

check this out.
Simplest 128 atmega programmer - Scientific, embedded, biomedical, electronics contents.

 

[hobbss]

That is not really what I am talking about. I have a programmer -- an AVRISP mkII that I will use to program the board. I am just concerned that I have PDO and PDI flipped.

 

[alexan_e]

There is only one place you need to look when you have a question like that (and it should be the first actually) and you can be sure that what is says is valid, not an assumption.

See page 350 of the datasheet www.atmel.com/dyn/resources/prod_documents/doc2549.pdf

You are using TQFP64 (ATMEGA1281), your connection is correct
I have attached a picture



I don't know the effect of the connection with the rs232 chip, the most secure method is a jumper that selects between programming and uart.
When you use a resistor like that the programmer has to be able to provide the current needed (because of the resistor) to force the value of the pin.

Alex

 

[alexan_e]

The chip which will be programmed is the slave,

The MOSI pin is Master Output Slave Input so it goes to the "serial data in"
The MISO pin is Master Input Slave Output so it goes to the "serial data out"

Alex

 

[hobbss]

That's what I thought (after checking the data sheet), but just wanted to verify (as I said, having been burnt once).