Traps are handled by an intricate loop. When the trap is called it executes something similar to a jump routine. With Pep/8 machines the instructions DECI, DECO, and STRO all call a trap. All content of the registers is pushed onto the system stack. Once the trap handler is complete control is returned to the application.
“A program during execution is called a process” (Warford, 2010, p. 397). When the trap is called the process is suspended. The operating system takes over to execute the trap handler. The process control block (PCB) is the block of memory that contains a copy of the trapped process’s registers. The statement RETTR returns control back to the process once the trap has completed. Any changes made in the PCB will change the registers in the CPU.
The DECI trap handler converts ASCII characters to bits in two’s complement. The handler will allocate six local variables on the stack. The variables are: total, valAscii, is0vfl, isNeg, state, and temp. A finite state machine loop is started. The bits go through the trap handler and bits are masked and multiplied with left-shift operations until the proper data is found. The DECO trap handler outputs decimal numbers. The trap is called and the data goes through a loop. The data is accessed with a load whereas the DECI is stored. The value is determined by repeatedly subtracting the variables place from remain. The trap handler for STRO uses stack-indexed deferred addressing. This process acts like an array in C++.
Traps on other machines offer operate similarly as the Pep/8 traps. “A trap handler is simply a function you write” (Becker, 2000). Some operating systems refer to traps as exceptions. Hyde (1996) explains that a trap is a program that transfers control to a special subroutine. All traps are unconditional, meaning that specific commands will always trigger a trap.

Warford, J. Stanley (2010). Computer Systems (4th ed.).
Hyde, Randall (1996) Interrupts, Traps, and Exceptions. Retrieved from http://flint.cs.yale.edu/cs422/doc/art-of-asm/pdf/CH17.PDF
Becker, Pete (2000) Trap handlers. Retrieved from http://www.petebecker.com/js/js200012.html