The Model 488 GPIB Analyzer is designed specifically to monitor and service abnormalities in IEEE-Standard-488-1978 General Purpose Interface Bus (GPIB) systems. The analyzer can be easily connected into any GPIB system (stack connector) for transparent analysis of the bus data. The analyzer features three operating modes: a. TRACE Mode; data is captured, stored in memory, and later displayed for analysis. b. PASSIVE Mode; presents the bus transactions in real time on the display. c. S/S (Single Step) Mode; allows bus transactions to be stopped or single-step. These modes are enhanced with ARM/STEP and START/END switches which increase flexibility by providing variations of the basic operation. The user is provided with three categories of data from the LCD (liquid-crystal-display) to visually interpret the bus data: a. Memory Location displays stored data locations in decimals digits 00 to 39. The display exhibits db (data bus) when directly viewing the bus. b. Data displays one of the 40 hexadecimal data bytes in memory or can display data from the bus. c. Bus line status indicators plus two analyzer status indicators, in addition to low battery and arm are also provided. The user can observe signals with short duration that are expanded with special pulse stretching circuits. The REN line is at logic one (0.8V) when the REN annunciator is displayed. The pulse stretcher turns it OFF for a visible period of time if the REN lines go to logic zero (2V) for 2 jus or longer. The IFC line is at logical one (0.8V), when the IFC annunciator is displayed. The pulse stretcher turns it ON for a visible period of time if the IFC line goes to a logic one (0.8V) for 2 jus or longer. The 488 Analyzer provides a terminal with 17 Test Points (TP) which parallels the GP1B connector. The 18th TP provides the trigger output for peripheral device. These TP connections expand the diagnostic applications of the analyzer. The 488 operates from a battery pack containing 4 C-type cells.