Hi All.
I'm designing a PCB incorporating dual-redundancy for RS-485 data processing and distribution. Involved in this, amongst other things, are relays which will need to be driven by both circuits (master, and slave if you will). However, should one of the processors go off-piste and drive a line high or low, it will prevent takeover by the other processor.
For this reason, instead of driving a line high (or low) to operate a transistor or optocoupler, I want to toggle a line.
Enter the watchdog timer. However these only assert for a brief, or defined, period. What I'm after is something that will output one state when the input is toggled, and another when it is stable (low OR high). In an ideal world it would have inverting and non-inverting outputs.
Toggling frequency isn't that important, I can do 2ms duty cycle up to 100's - instant response is not necessary to this usage case.
I realise this is basically a retriggerable monostable circuit, but I'm going to be pushed for space and putting >24 555's and supporting components per PCB is not really an option.
I feel like what I need almost exists in a WDT, but without 'permanent' assertion upon loss of input. There must be some IC, in an SOT-23 or similar that requires maybe 1 or 2 external components that does what I want, but I'm just not searching for the right thing.
Can anyone point me in the right direction?
Many thanks,
Tom.
I'm designing a PCB incorporating dual-redundancy for RS-485 data processing and distribution. Involved in this, amongst other things, are relays which will need to be driven by both circuits (master, and slave if you will). However, should one of the processors go off-piste and drive a line high or low, it will prevent takeover by the other processor.
For this reason, instead of driving a line high (or low) to operate a transistor or optocoupler, I want to toggle a line.
Enter the watchdog timer. However these only assert for a brief, or defined, period. What I'm after is something that will output one state when the input is toggled, and another when it is stable (low OR high). In an ideal world it would have inverting and non-inverting outputs.
Toggling frequency isn't that important, I can do 2ms duty cycle up to 100's - instant response is not necessary to this usage case.
I realise this is basically a retriggerable monostable circuit, but I'm going to be pushed for space and putting >24 555's and supporting components per PCB is not really an option.
I feel like what I need almost exists in a WDT, but without 'permanent' assertion upon loss of input. There must be some IC, in an SOT-23 or similar that requires maybe 1 or 2 external components that does what I want, but I'm just not searching for the right thing.
Can anyone point me in the right direction?
Many thanks,
Tom.