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Re: [avr-chat] Bus_Contention_Resistors

From: Joerg Wunsch
Subject: Re: [avr-chat] Bus_Contention_Resistors
Date: Fri, 8 Apr 2011 08:11:05 +0200 (MET DST)

John Sheley <address@hidden> wrote:

> I would like to know if someone has actually implemented this idea.

I don't think you need this with the AVRISPmkII device.  AFAICT, this
device already contains some logic to detect a bus contention, and
disconnects if it detects this situation (flashing the orange LED).

>  Also what is the maximum bus speed of the "AVRISP" 10MHz? 5MHz
> 3MHz?

AVRDUDE contains the following frequency table:

/* The list of SCK frequencies supported by the AVRISP mkII, as listed
 * in AVR069 */
static double avrispmkIIfreqs[] = {
        8000000, 4000000, 2000000, 1000000, 500000, 250000, 125000,
        96386, 89888, 84211, 79208, 74767, 70797, 67227, 64000,

So it's 8 MHz.  However, using 8 MHz requires a CPU running at more
than 32 MHz, which is not applicable for standard AVRs.  So the next
lower one is 4 MHz (requiring a CPU clock of more than 16 MHz to
operate), which you could use as the design base value for your

cheers, J"org               .-.-.   --... ...--   -.. .  DL8DTL

http://www.sax.de/~joerg/                        NIC: JW11-RIPE
Never trust an operating system you don't have sources for. ;-)

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