[En-Nut-Discussion] programming with stk500

[Harald Kipp]

>
>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