I found some threads about updating the STK500 with a new firmware and also some information about broken programmers, e.g. https://www.avrfreaks.net/index.p...
But I did not find too much information about the interaction between the two control devices, i.e. AT90S1200 and AT90S8535.
First I looked into the user guide for STK500 at
But on page 59 in the diagram was only one block called "control MCU".
So I had a closer look at the schematic (included in the latest AVRStudio help) or e.g. found at
Why this all?
Yesterday I noticed that our STK500 does not work anymore.
The red LED (main power) was on, the green LED was off at first. The status LED was dark (no color change from red, yellow, to green).
When I removed the VTARGET jumper the green LED turned on. First I thought there was some short circuit between VTG and GND.
But I could not establish a connection to the STK. Also still no reaction on the status LED.
Because the VTG is controlled by an adjustable voltage regulator (LM317) in combination with a low pass and the PWM of the 8535 I assume that the 8535 is broken.
I also looked on the SCK, MOSI lines while flashing the firmware with AVRprog tool of the AVR4.13Build528 (firmware STK500.ebn). The signals looked OK.
The programming procedure first seemed allright, but the verifying failed on the first memory position (0000 was read).
Now I am wondering, if it is really the 8535, in other words, if it is worth to unsolder this part.
I found in another thread, that the main task of the 1200 is, to put the 8535 in programming mode, for firmware updates. - OK, I also saw, that the 1200 monitors the push buttons PROGRAM an RESET.
(Q1) What does the 1200 else do? - Does it wait on a certain pattern on the RS232 CTRL and then put the /RESET line low during the whole 8535 firmware update???
(Q2) Can I replace the old obsolete AT90S8535-8AC of the STK500 by a newer ATMEGA8535L-8AC found in the AVRISP?
(Q3) If the AT90S1200-12SC is also broken, can I replace it by the ATTINY2313V-10SU, which is also used in the AVRISP?
(Q4) When programming external devices (especially with own voltage supply), may both controllers (1200, 8535) get easily broken/damaged, though there is also a transistor circuit to the ISP6PIN/ISP10PIN connectors (PBM5=>MOSIT, PBM6<=MISOT, PBM7=>SCKT)?
First I was a little confused because there are other SPI lines ("SPI-SP"), called DSI, DSO, DCK, DCS in the schematic. These lines are also going from the 8535 to some transistor circuit for amplifying and then to the extension slots.
When I put a STK501 in, I also use the SPROG connectors for programming.
(Q5) For what is this additional SPI-SP which goes from the 8535 to the EXPAND1/J701 connector?
Thank you for an answer and your experience,
P.S: I also looked at the application note 68 (STK500 Communication Protocol) at