Block Diagram for a difference equation I have this little doubt regarding how to draw a block diagram representation of a difference equation. Let us implement $ y(n) = ay(n-3) + by(n-2)+cy(n-1) + x(n)$ in block diagram where $a, b, c$ are constants. What I made is this.


Is this block diagram wrong? They say that you should use only $z^{-1}$ delay multiple times to produce the effect of $z^{-3}$ and $z^{-2}$. But I think that this diagram is also correct. Please help.
That's one way to do it but but typically you would have a single line of three delays in the feedback path and apply $a$ after the first delay, $b$ after the second and $c$ after the third.

And yes, you need arrowheads to make this clear.

By convention the coefficient of the feedback path would be called $a_1$, $a_2$, $a_3$ and the feed forward path would be $b_0$, $b_1$, etc. 

See for example https://www.researchgate.net/figure/Direct-Form-I-structure-of-IIR-filter_fig1_236688224