Can you help me write the code for the subroutines GetStringSB, PutStringSB, and PutNumU $?$ And can you kind of explain what you're doing and why it is what it is $?$ Thank you, I really appreciate your help $!!$

For reference this is what GetChar and PutChar basic info is:

GetChar: Reads a single character from the terminal keyboard into R$0.$

PutChar: Displays the single character from R$0$ to the terminal screen

GetChar

Input parameter: $($none$)$

Output parameter: R$0$: character received from terminal $($unsigned byte ASCII code$)$

PutChar

Input parameter: R$0$: character to send to terminal $($unsigned byte ASCII code$)$

Output parameter: $($none$)$