Heterozygous and Homozygous cross over on same chromosome?

It might help if you draw a picture of your chromosomes to see what happens.  It's also important to remember that when crossing over occurs, the chromosomes are doubled and the sister chromatids are still joined by their centromeres, and only the two chromatids that are next to each other but on different chromosomes actually cross over (see drawing) http://course1.winona.edu/kbates/Bio241/images/figure-09-16.jpg

So if your chromosomes are
R------S
R------S
r--------s
r--------s

when crossing over occurs, you'd get
R------S
R-------s
r--------S
r--------s

So that parent would produce a total of four possible gametes, RS, Rs, rS, and rs if crossing over is considered.

For the parent that's homozygous recessive, only one type of gamete is produced, even with crossing over:

r-----s
r-----s
r-----s
r-----s

So your Punnett square would be:

......|..rs..|
.RS.|
.Rs.|
..rS.|
..rs..|