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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
resistor.
--
cheers, J"org .-.-. --... ...-- -.. . DL8DTL
http://www.sax.de/~joerg/ NIC: JW11-RIPE
Never trust an operating system you don't have sources for. ;-)