The GPIB interface section consists of the SEC-1065 (Serial Control) and SER-1066 (Serial Register) modules. These modules provide the necessary hardware and control logic to remotely program an instrument via the GPIB (General Purpose Interface Bus) in accordance with the ANSI/IEEE Std 488.1-1987. The SEC and SER modules are unique and may not be interchanged with any other modules in the instrument. The two modules are piggy-backed and interconnected through a connector. Together, the boards are mechanically fastened to the instrument rear panel by four screws. The SEC module faces to the rear and contains a standard 24-pin GPIB connector and a six-position DIP switch for address and listen-mode selection. The SER module connects internally to the rest of the instrument through two header strips: one for frequency and amplitude control, and a second for phase rotation control. Functional Overview The basic data transfer on the GPIB is bit parallel, byte serial (one byte at a time), under the direction of a GPIB controller. The user typically provides the controller with information on the address of an instrument to be controlled, and any instrument-specific (also called devicedependent) instructions. The controller (or control program) will then generate a string of characters containing the ASCII codes for addressing the instrument and performing the instrument-specific function, and transmit these in conformance with the IEEE 488 timing and handshaking specifications. A PTS synthesizer equipped with the GPIB interface acts as a basic listener device. The standard LISTEN ONLY and ADDRESSED modes of operation are supported. In the LISTEN ONLY mode, all valid commands are accepted without regard to device address; in the ADDRESSED mode, only commands preceded by the instrument's selectable address are executed. In addition to LOCAL/REMOTE mode control, PTS's GPIB interface has the capability to perform three synthesizer-specific (or device-dependent) functions through appropriate commands issued over the GPIB: setting the output frequency, setting the output signal level, and setting phase rotation (for instruments equipped with a phase-rotation option).