ATtiny26(L)
	Latching of Fuses
		The fuse values are latched when the device enters programming mode and changes of
		the fuse values will have no effect until the part leaves programming mode. This does
		not apply to the EESAVE Fuse which will take effect once it is programmed. The fuses
		are also latched on Power-up in normal mode.

Signature Bytes

Calibration Byte

All Atmel microcontrollers have a three-byte signature code which identifies the device. This code can be read in both serial and parallel mode, also when the device is locked. The three bytes reside in a separate address space.

For the ATtiny26 the signature bytes are:

1.$000: $1E (indicates manufactured by Atmel).

2.$001: $91 (indicates 2KB Flash memory).

3.$002: $09 (indicates ATtiny26 device when $001 is $91).

The ATtiny26 stores four different calibration values for the internal RC Oscillator. These bytes resides in the signature row high byte of the addresses 0x0000, 0x0001, 0x0002, and 0x0003 for 1, 2, 4, and 8 MHz respectively. During Reset, the 1 MHz value is automatically loaded into the OSCCAL Register. If other frequencies are used, the calibration value has to be loaded manually, see “Oscillator Calibration Register – OSCCAL” on page 30 for details.

Page Size

Parallel Programming

Parameters, Pin

Mapping, and

Commands

Signal Names

Table 52. No. of Words in a Page and no. of Pages in the Flash

Flash Size	Page Size	PCWORD	No. of Pages	PCPAGE	PCMSB
1K words (2K bytes)	16 words	PC[3:0]	64	PC[9:4]	9

Table 53. No. of Words in a Page and no. of Pages in the EEPROM

EEPROM Size	Page Size	PCWORD	No. of Pages	PCPAGE	EEAMSB
128 bytes	4 bytes	EEA[1:0]	32	EEA[7:0]	7

This section describes how to parallel program and verify Flash Program memory, EEPROM Data memory, Memory Lock bits, and Fuse bits in the ATtiny26. Pulses are assumed to be at least 250 ns unless otherwise noted.

In this section, some pins of the ATtiny26 are referenced by signal names describing their functionality during parallel programming, see Figure 58 and Table 54. Pins not described in the following table are referenced by pin names.

The XA1/XA0 pins determine the action executed when the XTAL1 pin is given a positive pulse. The bit coding is shown in Table 56.

When pulsing WR or OE, the command loaded determines the action executed. The different Commands are shown in Table 57.

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Figure 58. Parallel Programming

WR

+5V

PB0

VCC

XA0

PB1

+5V

XA1/BS2

PB2

AVCC

PAGEL/BS1

PB3

DATA

PA7: PA0

PB5

OE

PB6

RDY/BSY

+12 V RESET

XTAL1/PB4

GND

Table 54. Pin Name Mapping

	Signal Name in
	Programming Mode					Pin Name	I/O	Function
						PB0	I	Write Pulse (Active low)
	WR
	XA0					PB1	I	XTAL Action Bit 0
	XA1/BS2(1)					PB2	I	XTAL Action Bit 1 multiplexed with Byte Select 2
								(“0” selects low byte, “1” selects 2’nd high byte)
	PAGEL/BS1(1)							Program Memory and EEPROM data Page Load
						PB3	I	multiplexed with Byte Select 1 (“0” selects low
								byte, “1” selects high byte).
						PB5	I	Output Enable (Active low)
	OE
								0: Device is busy programming, 1: Device is ready
	RDY/BSY					PB6	O
								for new command
	DATA					PA7:0	I/O	Bidirectional Data bus (Output when		is low)
									OE

Note: 1. The pin is used for two different control signals. In the description below, normally only one of the signals is referred. E.g., “give BS1 a positive pulse” equals “give PAGEL/BS1 a positive pulse”.

Table 55. Pin Values used to Enter Programming Mode

	Pin		Symbol	Value
	PAGEL/BS1		Prog_enable[3]	0
	XA1/BS2		Prog_enable[2]	0
	XA0		Prog_enable[1]	0
			Prog_enable[0]	0
	WR

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ATtiny26(L)

Table 56. XA1 and XA0 Coding(1)

XA1	XA0		Action when XTAL1 is Pulsed
0	0		Load Flash or EEPROM Address (High or low address byte determined by
			BS1).
0	1		Load Data (High or Low data byte for Flash determined by BS1).
1	0		Load Command
1	1		No Action, Idle
Note:	1.	[XA1, XA0] = 0b11 is “No Action, Idle”. As long as XTAL1 is not pulsed, the Com-
		mand, Address, and Data Registers remain unchanged. Therefore, there are no
		problems using BS2 as described below even though BS2 is multiplexed with XA1.
		BS2 is only asserted when reading the fuses			is low) and XTAL1 is not pulsed.
				(OE

Table 57. Command Byte Bit Coding

Command Byte	Command Executed
1000 0000	Chip Erase
0100 0000	Write Fuse Bits
0010 0000	Write Lock Bits
0001 0000	Write Flash
0001 0001	Write EEPROM
0000 1000	Read Signature Bytes and Calibration Byte
0000 0100	Read Fuse and Lock Bits
0000 0010	Read Flash
0000 0011	Read EEPROM

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