The TEKTRONIX 7B90P Programmable Time Base provides calibrated sweep rates for TEKTRONIX 7000-Series programmable mainframes. The 7B90P may be inserted in any 7000-Series mainframe without damage, but is recommended for use only in a programmable mainframe. The 7B90P has calibrated sweep rates ranging from 500 picoseconds/ division to 500 milliseconds/division. Other operating features that can be selected are: normal or automatic triggering, high or low frequency roll-off (attenuation) of the triggering signal, variable trigger hold-off, internal or external triggering, 1X or 10X sweep magnification, and repetitive or single-sweep mode. The 7B90P has readout encoding capability. Thus, horizontal scale factors can be displayed on a programmable mainframe having readout display capability. All functions of the 7B90P can be remotely programmed except for the Sweep Calibration (SWP CAL) adjustment and the External Trigger Input Termination (TERM) switch. The status of each programmable function can be set or read by commands sent over the IEEE 488 bus. These commands can be sent in either a high-level or low-level language, Doth of which are decoded by a microprocessor in the 7B90P.