From 378d5da5a89be0dc2c95d4d6d33d8420d5dadd6d Mon Sep 17 00:00:00 2001 From: Christian Starkjohann Date: Mon, 20 Oct 2008 16:54:58 +0000 Subject: - mentioned 12.8 MHz module --- usbdrv/Readme.txt | 24 ++++++++++++------------ 1 file changed, 12 insertions(+), 12 deletions(-) (limited to 'usbdrv/Readme.txt') diff --git a/usbdrv/Readme.txt b/usbdrv/Readme.txt index 96a79d0..f846689 100644 --- a/usbdrv/Readme.txt +++ b/usbdrv/Readme.txt @@ -47,9 +47,9 @@ The driver consists of the following files: CPU CORE CLOCK FREQUENCY ======================== -We supply assembler modules for clock frequencies of 12 MHz, 15 MHz, 16 MHz and -16.5 MHz. Other clock rates are not supported. The actual clock rate must be -configured in usbdrv.h unless you use the default 12 MHz. +We supply assembler modules for clock frequencies of 12 MHz, 12.8 MHz, 15 MHz, +16 MHz, 16.5 MHz and 20 MHz. Other clock rates are not supported. The actual +clock rate must be configured in usbdrv.h unless you use the default 12 MHz. 12 MHz Clock This is the traditional clock rate of AVR-USB because it's the lowest clock @@ -67,15 +67,15 @@ if you need the slightly higher clock rate for performance reasons. Since 16 MHz is not divisible by the USB low speed bit clock of 1.5 MHz, the code is somewhat tricky and has to insert a leap cycle every third byte. -16.5 MHz Clock -The assembler module for this clock rate differs from the other modules because -it has been built for an RC oscillator with only 1% precision. The receiver -code inserts leap cycles to compensate for clock deviations. 1% is also the -precision which can be achieved by calibrating the internal RC oscillator of -the AVR. Please note that only AVRs with internal 64 MHz PLL oscillator can be -used since the 8 MHz RC oscillator cannot be trimmed up to 16.5 MHz. This -includes the very popular ATTiny25, ATTiny45, ATTiny85 series as well as the -ATTiny26. +12.8 MHz and 16.5 MHz Clock +The assembler modules for these clock rates differ from the other modules +because they have been built for an RC oscillator with only 1% precision. The +receiver code inserts leap cycles to compensate for clock deviations. 1% is +also the precision which can be achieved by calibrating the internal RC +oscillator of the AVR. Please note that only AVRs with internal 64 MHz PLL +oscillator can reach 16.5 MHz with the RC oscillator. This includes the very +popular ATTiny25, ATTiny45, ATTiny85 series as well as the ATTiny26. Almost +all AVRs can reach 12.8 MHz, although this is outside the specified range. See the EasyLogger example at http://www.obdev.at/avrusb/easylogger.html for code which calibrates the RC oscillator based on the USB frame clock. -- cgit v1.2.3