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Honored ContributorHow to set to 0 value unconnected input pin?
Hi!
In my design, some FPGA inputs could be left unconnected. But the value of this unconnected pins must be 0. I've found out that by default this pins are set to 1. So it is force me to connect output source to all pins, otherwise it won't work properly. The question is, how could I set this temporary unused pins to 0? I use Quartus II. Thank you!7 Replies
Altera_Forum--- Quote Start --- Hi! In my design, some FPGA inputs could be left unconnected. But the value of this unconnected pins must be 0. I've found out that by default this pins are set to 1. So it is force me to connect output source to all pins, otherwise it won't work properly. The question is, how could I set this temporary unused pins to 0? I use Quartus II. Thank you! --- Quote End --- Wouldn't it simply to just set your pins as GND source instead of VCC on your input pins?- Altera_Forum--- Quote Start --- Wouldn't it simply to just set your pins as GND source instead of VCC on your input pins? --- Quote End --- true. The unused pins are set in project assignments => device => device and pin options => unused pins There are several options: 1) default(hopefully) "as tristated inputs with weak pullup", Quartus connects it to Vcc internally, no need for pcb wiring to Vcc 2) "as tristated inputs", you need to connect to board Vcc or ground 3) "as output driving ground", quartus connects it to gnd internally, no need for wiring to pcb gnd. This is what you are after, provides more ground. 4) "as outputs driving unspecified signal", 5) "as tristated inputs with bus hold circuitry" I am not clear about last two but assume it means floating, this is bad , consumes extra power and acts as antennas for noise.
- Altera_Forum
Thank you for your quick replies!
--- Quote Start --- Wouldn't it simply to just set your pins as GND source instead of VCC on your input pins? --- Quote End --- I think that is what i'm trying to do. But i don't know how to do it internally in Quartus II or by scripting. I'm totally beginner. --- Quote Start --- The unused pins are set in project assignments => device => device and pin options => unused pins There are several options: 1) default(hopefully) "as tristated inputs with weak pullup", Quartus connects it to Vcc internally, no need for pcb wiring to Vcc 2) "as tristated inputs", you need to connect to board Vcc or ground 3) "as output driving ground", quartus connects it to gnd internally, no need for wiring to pcb gnd. This is what you are after, provides more ground. 4) "as outputs driving unspecified signal", 5) "as tristated inputs with bus hold circuitry" --- Quote End --- I have tried to set "as output driving ground" to all unused pins, but when I do it, the programmer tool fails to program my device. I can't quite understand whether unused pins, are all those pins that are assigned in pin planner but not wired on board, or those are pins that are not assigned in pin planner at all? I mean, I want to use pin as ordinary input but when I unplug connector to it, the pin value should be 0. And unfortunately there is no pull-down resistor. - Altera_Forum--- Quote Start --- I have tried to set "as output driving ground" to all unused pins, but when I do it, the programmer tool fails to program my device. I can't quite understand whether unused pins, are all those pins that are assigned in pin planner but not wired on board, or those are pins that are not assigned in pin planner at all? I mean, I want to use pin as ordinary input but when I unplug connector to it, the pin value should be 0. And unfortunately there is no pull-down resistor. --- Quote End --- Unconnected pins are those not used by you (not wired internally) so the unused options don't apply to your case. You can apply '0' internally provided you have some switch tied up to the connector. when connector is in it drives the pin else it is driven internally by your logic.
- Altera_Forum--- Quote Start --- Unconnected pins are those not used by you (not wired internally) so the unused options don't apply to your case. You can apply '0' internally provided you have some switch tied up to the connector. when connector is in it drives the pin else it is driven internally by your logic. --- Quote End --- Thank you! It is clear to me now.
- Altera_Forum--- Quote Start --- true. The unused pins are set in project assignments => device => device and pin options => unused pins There are several options: 1) default(hopefully) "as tristated inputs with weak pullup", Quartus connects it to Vcc internally, no need for pcb wiring to Vcc 2) "as tristated inputs", you need to connect to board Vcc or ground 3) "as output driving ground", quartus connects it to gnd internally, no need for wiring to pcb gnd. This is what you are after, provides more ground. 4) "as outputs driving unspecified signal", 5) "as tristated inputs with bus hold circuitry" I am not clear about last two but assume it means floating, this is bad , consumes extra power and acts as antennas for noise. --- Quote End --- Hi kaz, Does item 3) make hardware dangerous? At least cause more power consumption.
- Altera_Forum--- Quote Start --- Hi kaz, Does item 3) make hardware dangerous? At least cause more power consumption. --- Quote End --- more power, yes somewhat but floating consumes even more power. dangerous? I don't expect Altera to have that setting then for their devices.
