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Discussion Groups | TMS320C54x | Re: C5x inputs
Technical discussions about the TI C54x DSPs (including the c5401, c5402, c5402a, c5404, c5407, c5409, c5409a, c5410, c5410a, c5416, c5420, c5421, c5441, c549, c5470 and c5471).
C5x inputs - Les Newell - Sep 13 15:51:00 2002
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Hi, Is it essential to tie lines such as unused IRQs high via a resistor? Is there any reason why they can't be tied directly to the +3.3V rail? TIA, Les |
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Re: C5x inputs - Jeff Brower - Sep 13 17:10:00 2002
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Les Newell- > Is it essential to tie lines such as unused IRQs high via a resistor? Is > there any reason why they can't be tied directly to the +3.3V rail? Not sure about IRQs off the top of my head, but I can tell you that if you pull up any line that can also be programmed as GPIO, those should be done separately from other pull-ups. The reason is that sometimes during boot GPIO lines may temporarily act as uninitialized outputs, and can thus be low. If such a transient low pulls down another line tied in common, such as HMODE, XIO, etc. then you will have a serious problem. I know; we encountered this last year with a multiple C5421 board. Jeff Brower DSP sw/hw engineer Signalogic |
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Re: C5x inputs - Les Newell - Sep 13 17:52:00 2002
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Thanks Jeff, If I remember correctly I am uisng all the GPIO lines so this should not be a problem. However, I will add it to my "must remember when designing boards" list! Les > Les Newell- > > > Is it essential to tie lines such as unused IRQs high via a resistor? Is > > there any reason why they can't be tied directly to the +3.3V rail? > > Not sure about IRQs off the top of my head, but I can tell you that if you pull up > any line that can also be programmed as GPIO, those should be done separately from > other pull-ups. The reason is that sometimes during boot GPIO lines may temporarily > act as uninitialized outputs, and can thus be low. If such a transient low pulls > down another line tied in common, such as HMODE, XIO, etc. then you will have a > serious problem. I know; we encountered this last year with a multiple C5421 board. > > Jeff Brower > DSP sw/hw engineer > Signalogic > > _____________________________________ |
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Re: C5x inputs - softguy GSS - Sep 16 1:40:00 2002
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Hi Les, In my designs using C54xx CPU, all maskable interrupts had been left floating and made sure that these interrupts were disabled. NMI was pulled high through a pullup resistor. Actually TI wont suggest us to tie any of the input lines directly to 3.3V rail. Rather suggest us to tie all the pins which are not being used high through a common resistor. (resistor value should be scaled as per the no of input pins being tied high). Good luck, -Sreevathsa --- Les Newell <> wrote: > Hi, > > Is it essential to tie lines such as unused IRQs > high via a resistor? Is > there any reason why they can't be tied directly to > the +3.3V rail? > > TIA, > Les > > _____________________________________ __________________________________________________ |
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