shift register - simple q

Started by limorgarcia December 9, 2003
is it possible to shiftout "nothing" to a shift register? meaning if
i have a line of code that is shifting out bytes to several daizy-
chained shift registers, and then i need to shiftout data to only
the third shift register in the chain, is it possible without
effecting the other shift registers?
thank you



No. You have to shift it a line of 0's (or 1's, depending on your
definition of nothing) On Dec 9, 2003, at 12:20 AM, limorgarcia wrote:

> is it possible to shiftout "nothing" to a shift register? meaning if
> i have a line of code that is shifting out bytes to several daizy-
> chained shift registers, and then i need to shiftout data to only
> the third shift register in the chain, is it possible without
> effecting the other shift registers?
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Tom Igoe


--- In , "limorgarcia" <limorgarcia@y...> wrote:
> is it possible to shiftout "nothing" to a shift register? meaning
if
> i have a line of code that is shifting out bytes to several daizy-
> chained shift registers, and then i need to shiftout data to only
> the third shift register in the chain, is it possible without
> effecting the other shift registers?

If this ability is a requirement, you could redesign the circuit so
that the shift registers are independently clocked. All the SRs
could share the same data line but you'd need a separate clock for
each. If you have the I/O pins available, the simplest way would be
to use a different I/O pin for each shift register clock. To reduce
the number of pins used, you can use a demultiplexer/decoder (e.g.
74LS138). Three I/O pins could specify which of 8 registers to clock
and a fourth pin would strobe the enable of the decoder to produce
the clock pulse.

Don


At 05:04 PM 12/9/2003 -0000, you wrote:
> is it possible to shiftout "nothing" to a shift register? meaning
if > i have a line of code that is shifting out bytes to several daizy-
> chained shift registers, and then i need to shiftout data to only
> the third shift register in the chain, is it possible without
> effecting the other shift registers?

<---What you could do is to use a registers that have a latch control line
(like a 74HC595) and control each latch independently. That way, only the
one(s) you select to change states will, with the latched one remaining in
it's previous state.

Ken
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