Grade is an unsigned byte stored in the PM$.$ Letter is a byte stored in SRAM and based on the integer value in Grade. Letter $="$A$","$B$","$C$","$D$",$ or $"$F$"$ based on the value in Grade: $89<$ A; $79<$ B $<90$; $69<$ C $<80$; $59<$ D $<60$; F $<60$ on michrochip assembly