Table of Contents
Advertisement
Micro-ISP
Atmel AT90S/ATtiny - ISP Notes
1. RESET circuit
This should be an 'Active
LOW' RESET circuit. To
prevent inevitable EEPROM
corruption, an electronic
brownout circuit is
recommended such as a
'RESET Supervisor' device
available from Dallas
Semiconductor, Maxim, Seiko
etc.
2. SCK connection
This is an output from the
programmer and an input to
the target device during
programming. It is
recommended that this pin is
only used as an input on the
user target circuit. However,
it should still be possible to
program the device even if
the pin is set to an output by
user firmware.
3. Protection resistors
It is good EMC design practice to place some limiting resistance on each processor I/O line to
protect against damage from transients. i.e. R2, R3, R4, R5. A very low value of e.g. 10
ohms is recommended. Further protection can be afforded by using ferrites instead of
resistors. The ATmega devices are very sensitive to the voltage slew rate, so use of any
component which slews the edges of the programming signals may cause unreliable
programming.
4. SCK Noise filtering
If noise spikes on the SCK pin are found to be a problem, a resistor i.e. R6 may be inserted
between the SCK pin and ground.
5. Active LED
An LED may be placed on the user target system to indicate when the programmer is active.
The value of R7 should be chosen to suit the target supply voltage.
IV User Manual V2.03
Series
Active LOW
RESET Circuit
XT1
C1
Further sources of information:
AN102 - ISP Design Notes for the Atmel ATtiny (AVR)
Microcontroller Family
C6
Vcc
RESET
ATMEL
AT90SXXXX
Microcontroller
Interrupt
P3
8
PD.0-PD.7
P2
8
PC.0-PC.7
USER
P1
I/O
PB.0-PB.4
5
P0
8
PA.0-PA.7
XTAL1
XTAL2
GND
C2
25
R2
Vcc
C4
R1
U1
Pin
PB.7
SCK
R3
PB.6
MOSI
R4
PB.5
MISO
R5
PROG-RESET
PROG-VCC
LED1
PROG-ACTIVE
PROG-SCK1
PROG-MOSI
PROG-MISO
PROG-GROUND
Advertisement
Table of Contents
