I have just started using the DVK90CAN1 & ported some ATMega128 code to it and having some problems.
To solve these, I wrote some code which continuously sens a question mark (0x3f) to UART1m which I want to see using Hyperterminal.
OK, that all that seems straight forward.
When I power up, it sends ?'s for about two seconds and then starts to send gibberish. If I then press reset it stops sending gibberish & about five seconds later it sends more gibberish with the reset still pressed. :o
I have come to the conclusion that the MAX3232 is the culprit. It has about a 1 V P-P charge pump noise on the + & -ve supply. Is this normal?? I have never had any problems like that on MAX232 or MAX232A.
When I reset and hold it reset, the charge on the TXD0 line slowly discharges and then the RS-232 line starts to put out continuous START bit.
I have decoupled the MAX3232 with an extra 1uF Tantalum, but it has had no effect.
Do I have a crook DVK90CAN1 board or crook MAX3232 or is this a common problem.
Lee de Vries
Further test, indicate that I can receive data at all time , by writing data to PORTA LEDS. However except for the first two seconds of power up, echoed data is not responded to by Hyperterminal.
I then used a notebook and I can get more data transfer , but it was marginal & intermittant.
So, I suspect that it is a noise margin problem where the problem is worse because the data transceivers run at +&- 12 V.
Inspecting the data sheet dor the MAX3232 , suggest for a Vcc of +5 Volts C2,C3 & C4 should be 0.33 uF
minimum. So is it a botched design by ATMEL on the DVK90CAN1 board.
Opinions saught. I have another 7 of these boards on order! :(