Equinox Systems Micro-ISP IV Series User Manual page 30

Micro-ISP
Atmel AT89S/89LS - ISP Notes continued
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.
Warning !
To avoid lock-up of the target device:
- Avoid writing a ZERO to the SCK pin within 700ms of coming out of RESET.
- Do not use the SCK pin as an output in your own target system.
If the target device will not re-program, connect the EA pin to ground by moving J1 to
position 2-3 and then try to re-program. Remove any writes to the SCK pin within your
software!
Further sources of information:
AN103 - ISP Design Notes for the Atmel AT89S/89LS Microcontroller Family
IV User Manual V2.03
Series
23