EPF10K10 and CPU reset using INIT_DONE

[Altera_Forum]

Hi There! 

 Yes, I'm using an EPF10k10 :-) So I'm considering using INIT_DONE to hold my Z80 in reset during configuration. I'd also like to be able to manually reset, so I'd like to know if I can just add a switch to ground between the 1k pull-up and INIT_DONE.    There's some ambiguity as to whether or not the pin will tri-state or not, hence my question. To clarify:    ^ vcc  |  /   \ 1K  /  +------------ INIT_DONE (also connected to z80 reset )  |  |  / NO switch  /  |  |  + gnd   anyone see anything wrong with this? The Z80 will make sure the FPGA registers will be reset using a regular write.   Cheers,   -Mux

[Altera_Forum]

A slight alternative to your approach is to use a reset supervisor IC. For example, look on page 95: 

 http://www.ovro.caltech.edu/~dwh/carma_board/gda06rb004_carma_v0.87_dec03.pdf  The inputs to the reset supervisor are;  1) A front panel push-button reset 2) PCI reset 3) CONF_DONE from the system controller FPGA  (you could also use INIT_DONE).   The CONF_DONE signal drives a tri-state buffer to ensure that it drives the reset input open-drain. If INIT_DONE is driven, then you can use the same approach for your circuit.  Using a reset supervisor has the added advantage when dealing with a push-button of debouncing the signal.  If you only have your CPU and INIT_DONE as the reset sources, then you would not need the reset supervisor, however, you might want to use the tri-state drivers to create a common reset with multiple drivers.  Cheers, Dave

[Altera_Forum]

Hi! 

 Thanks for the reply!  While a reset supervisor is definitely handy, I think it's a little overkill for my project famous last words) That said, adding a cap between GND and the switch should take care of debouncing.  To verify: After configuration, does INIT_DONE go tristate or high / low? I'm assuming it's tristating..  -Mux

[Altera_Forum]

--- Quote Start ---   To verify: After configuration, does INIT_DONE go tristate or high / low? I'm assuming it's tristating..   --- Quote End ---    p68 indicates that INIT_DONE is open-drain:  http://www.altera.com/literature/hb/cfg/cfg_cf51005.pdf  Its driven low until configuration completes. Its up to you to supply the external pull-up to make it go high.  Cheers, Dave

[Altera_Forum]

Thanks Dave!