AVR Tiny26

The manual of the Tiny26 (Rev 1477G-AVR-03/05) is somewhat intransparent and distributes the relevant information over many pages.

the fuses

The programming fuses are

fuse	default	meaning	page
RSTDISBL	1	Reset disable =0, pin becomes PB7, further programming requires parallel mode programmer	108
CKSEL3..0	0001	internal, external, ceramic, RC, crystal	24,27
PLLCK	1	adds an internal 64MHz PLL for use between 4.5 and 5.5V, Systemclock will be 16MHz then	24,30
CKOPT	1	clock amplifier for crystal oscillator or so, depends on the clocksource itself, CKOPT=0 for higher amplitudes	25
SUT1..0	10	startup time selector	26,27,28,29,30
SPIEN	0	enable SPI programming mode	108
JTAGEN	0	enable JTAG programming	254
EESave	1	preserve EEPROM through chip erase	108
BODLEVEL	1	brownout detection on 2.7V = 1, or 4.0V = 0	35,37
BODEN	1	brownout detection enabled = 0, hysteresis will be 50mV	37

Concerning the fuses, 0 means programmed and 1 means unprogrammed.

Clock Options

The tiny26 offers the following clock options. page 24

Device clocking option	PLLCK	CKSEL3..0
External crystal/ceramic resonator	1	1111-1010
External low frequency crystal	1	1001
External RC	1	1000-0101
Calibrated internal RC	1	0100-0001
External clock	1	0000
PLL Clock	0	0001

default clock source

The device is shipped with CKSEL3..0 = 0001 and SUT1..0 = 10, an internal RC with the longest startup time. page 25.

crystal oscillator

This mode allows for either a crystal or a ceramic resonator. When CKOPT=0, then the Osc output at XTAL2 is being driven rail-rail. When not programmed (=1), then the swing is smaller, the frequency range is limited and the powerrconsumption is lower.
For resonators, the max frequency is 12MHz with CKOPT=1 and CKOPT=0 should not be used for resonators.

Crystal oscillator operating modes, page 25

CKSEL3..1	freq range MHZ	recommended caps
101	0.4 - 0.9	for resonators only
110	0.9 - 3.0	12 - 22pF
111	3.0 - 16.0	12 - 22pF
111	16 -	12 - 15pF

Startup times for the crystal oscillator clock selection, page 26

CKOPT	CKSEL0	SUT1..0	startup time	additional reset delay	recommended usage
1	0	00	258 clk	4.1ms	ceramic, fast rising power, not frequency stable at startup
1	0	01	258 clk	65ms	ceramic, slow rising power, not frequency stable at startup
1	0	10	1k clk	-	ceramic, BOD enabled, frequency stable at startup
1	0	11	1k clk	4.1ms	ceramic, fast rising power, frequency stable at startup
1	1	00	1k clk	65ms	ceramic, slow rising power, frequency stable at startup
x	1	01	16k clk	-	crystal, BOD enabled
x	1	10	16k clk	4.1ms	crystal, fast rising power
x	1	11	16k clk	65ms	crystal, slow rising power

Low frequency crystal oscillator

This clock option is to use a 32768Hz crystal. Set the CKSEL=1001. Programming the CKOPT=0 enables internal 36pF between XTAL1 and GND and between XTAL2 and GND. Startup times for the low frequency crystal oscillator, page 26

SUT1..0	Startup from powerdown & powersave	additionaldelayfrom reset @ Vcc=5V	recommended usage
00	1k clk	4.1ms	fast rising power or BOD enabled
01	1k clk	65ms	slowly rising power
10	32k clk	65ms	Stable frequency at startup
11	reserved	reserved	reserved

option 00 and option 01 should only be used if frequency stability at startup is not important

External RC oscillator

The frequency is roughly 1/(3*R*C), with C at least 22pf between XTAL1 and GND.
The CKOPT fuse enables the internal 36pF cap between XTAL1 and GND.
and thus remove the need for an external capacitor. Frequency selection, page 27

CKSEL3..0	Nominal frequency
0101	<= 0.9 MHz
0110	0.9 - 3.0 MHz
0111	3.0 - 8.0 MHz
1000	8.0 - 12.0 MHz

Startup times for the external RC oscillator, page 27

SUT1..0	Startup from powerdown & powersave	additionaldelayfrom reset @ Vcc=5V	recommended usage
00	18clk	-	BOD enabled
01	18clk	4.1ms	fast rising power
10	18clk	65ms	Slowly rising power
11	6clk	4.1ms	fast rising power or BOD enabled

option 11 should not be selected close to the max frequency of the device

Calibrated internal RC oscillator

Set CKOPT=1
Frequency selection, page 28

CKSEL3..0	Nominal frequency
0001	1.0 MHz
0010	2.0 MHz
0011	4.0 MHz
0100	8.0 MHz

The 0001 is factory default.

Startup times for internal calibrated RC oscillator, page 28

SUT1..0	Startup from powerdown & powersave	additionaldelayfrom reset @ Vcc=5V	recommended usage
00	6clk	-	BOD enabled
01	6clk	4.1ms	fast rising power
10	6clk	65ms	Slowly rising power
11	reserved	reserved	reserved

option 10 is default when shipped.
The calibration value is written to register OSCCAL.

Internal RC Osc calibration value, page 28, 29

OSCCAL value	min frequency in percentage from nominal	max frequency in percentage from nominal
$00	50	100
$7F	75	150
$FF	100	200

The RC oscillator is intended for 1.0, 2.0, 4.0 or 8.0MHz. Calibrating it to other frequencies is not guaranteed.

external clock

Connect the external oscliiator to XTAL1 while leaving the XTAL2 open.
Set Cksel3..0=0000, CKOPT is 1 or a 36pf cap is enabled between XTAL1 and GND.

Startup times for external clock, page 29

SUT1..0	Startup from powerdown & powersave	additionaldelayfrom reset @ Vcc=5V	recommended usage
00	6clk	-	BOD enabled
01	6clk	4.1ms	fast rising power
10	6clk	65ms	Slowly rising power
11	reserved	reserved	reserved

High Frequency PLL

Programming the PLLCK=0 enables an internal PLL at 64MHz based on the RC Oscillator. The system clock is divided by 4, and thus is 16MHz. The PLL requires the CKSEL3..1 to be "0001" and the supply has to be between 4.5 and 5.5V for reliable operation. The SUT1..0 fueses determine the startup time. page 30

SUT1..0	Startup from powerdown & powersave	additionaldelayfrom reset @ Vcc=5V	recommended usage
00	1k CK	-	BOD enabled
01	1k CK	4.1ms	fast rising power
10	1k CK	65ms	Slowly rising power
11	16k CK	-	slowly rising power

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last updated 28.June.06 or perhaps later

Copyright (99,2006) Ing.Büro R.Tschaggelar