Write in LC-2 assembler, using the device registers introduced in chapter 8, a program that reads characters from the terminals and echoes input lower-case letters back to the monitor. All other charcters are ignored.
This answer was provided by Bryan Powell and slighted edited by me.
START LDI R1,KBSR ; Test the status register BRzp START LDI R0,KBDR ; Read the character into R0 LD R1,aNEG ADD R1,R1,R0 BRn START ; Don't print if < 'a' LD R1,zNEG ADD R1,R1,R0 BRp START ; Don't print if > 'z' ECHO LDI R1,CRTSR ; Print it here BRzp ECHO STI R0,CRTDR BR START KBSR .FILL xF400 KBDR .FILL xF401 CRTSR .FILL xF3FC CRTDR .FILL xF3FF aNEG .FILL #-97 ; -'a' zNEG .FILL #-122 ; -'z' .END