Michael S. Wolfberg_and Robb N. Russell, The Moore

School of Electrical Engineering, University of Pennsylvania,

Philadelphia, Pennsylvania

DDT-UP is an octal-symbolic debugging program for a 4K

PDP-8 which occupies locations 5600-7667. The mnemonics

for the eight basic instructions are defined internal to this

area. Other symbols are stored, four locations per symbol,

from 5577 down towards 0000. The mnemonics for the standard

OPR and IOT group instructions are initially defined in this

area. Thus, the highest location initially available to the

user is 5363. Beginning at this location the user may define

symbols one at a time using the comma(,) operator.

From the Teletype, the user can symbolically examine and

modify the contents of any memory location. DDT-UP

allows the user to punch a corrected program in CBL format.

DDT-UP has a breakpoint facility to help the user run sections

of his program. When this facility is used the debugger also

uses location 0005.