Gunning transceiver logic (GTL) is a type of logic signaling used to drive electronic backplane buses. It has a voltage swing between 0.4 volts and 1.2 volts — much lower than that used in TTL and CMOS logic — and symmetrical parallel resistive termination. The maximum signaling frequency is specified to be 100 MHz, although some applications use higher frequencies. GTL is defined by JEDEC standard JESD 8-3 (1993) and was invented by William Gunning while working for Xerox at the Palo Alto Research Center.