Dataman 448PRO2 User Manual page 161

Please, read some notes for following recommended circuits.
Purpose of D1 diode is to protect the target circuit against a higher voltage, which is provided
by ISP programmer.
If your target board supply differs from mentioned 5V, choose please the Zener diode (D1)
voltage according to this supply voltage.
We recommend using resistors R1, R2, (R3) to separate the target device from target
system. If pins needed for ISP programming are inputs in target system then separation by
resistors is sufficient and resistors make a low pass filter too. If pins are outputs, then use of
resistors saves a programming time. Of course the isolation resistors R1, R2, (R3) can be
replaced by switches or jumpers, if necessary. In that case, during the ISP programming of
target device the switches (jumpers) must be open. But the using of switches (jumpers) adds
a next manipulation time to programming procedure.
Example of application note
Microcontrollers Atmel AVR and AT89Sxxx series
This interface corresponds with Atmel application note AVR910: In-System Programming. This
application note describes the recommended ISP interface connector layout in target system
(top view).
DATAMAN recommended circuit for ATMEL AVR:
ISP connector
DATA IN
DATA OUT
SCK
RESET
target VCC check only
GND
D2
1N4148
R11
100k
C2
1u/10V
GND
reset circuit
target device
C1
22n
GND
VCC
MOSI
MISO
SCK
RESET
I1
ATMEL AVR
GND
GND
161
Common notes
target system
VCC
R1
R2
R3
GND