[En-Nut-Discussion] programming with stk500

[Louis Beaudoin]

I made this modification to my Atmel AVRISP programmer for programming 
my Ethernut 1.x board, it should work the same for the STK500.  I cut 
the traces connecting pin 3 (Ethernut: PROG ENABLE, Atmel: N/C) to 
ground on the programmer.  Then I soldered a wire between pin 3 and pin 
5 (RESET) so the reset signal would also be on pin 3.  This had the 
effect of driving PROG ENABLE low while reset was low, allowing me to 
program the board without using a jumper on JP4.

Louis



Harald Kipp wrote:
> 
>>
>> I think seting the Jumper J4 set the Programming mode, isnt it?
> 
> 
> No. The ATmega128 is a bit special. It shares the programming
> lines PDI/PDO with the UART0 lines RxD/TxD. During programming,
> the output of the RS232 driver drives against the programmer's
> (e.g. STK500) output on the PDI line. Therefore, Ethernut 1.3F
> got a multiplexer, swiching the CPU's PDI line between the
> ISP connector and the RS232 driver. This multiplexing is controlled
> by the PROG ENABLE, but the STK500 board doesn't provide this
> signal. Setting JP4 (the jumper near the ISP connector) switches
> the multiplexer, so the PDI is removed from the RS232 driver and
> connected to the ISP connector. As long as JP4 is set, UART0
> receiving is disabled. So you don't need to remove the jumper
> unless your application reads from uart0.
> 
> The ATmega is set into programming mode by holding down
> the reset line and sending specific codes to the PDI line.
> The reset line should be pulled low by the STK500 board during
> programming.
> 
> 
>> > Ethernut 1.3 Rev-G doesn't require PROG ENABLE, but uses the
>> > RESET signal to disable the RS232 driver.
>>
>> If i have this board whitch consequences are resulting for the 
>> programming
>> prozess?
> 
> 
> Because the RESET line disables the RS232 driver output
> (puts it in z-state), no multiplexing is required.
> 
> Harald
> 
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