A system for transmitting and receiving serial data over a pair of differential lines so that relatively large differences in ground potential will not affect the integrity of the transmitted data. Each differential line has a first switch for pulling the line high and a second switch for pulling the line low. Logical gates hold all switches off to allow the lines to float in response to a first control signal. A second control signal enables the logical gates to pull the first differential line up and the second differential line down whenever true data is to be sent and for pulling the second differential line up and the first differential line down whenever data is true. Associated with each switch is a protective diode and cold filament lamp for protecting the respective switch and insuring system operation even if large swings in ground potential occur. A differential amplifier has one input resistively coupled to the first differential line and a second input resistively coupled to the second differential line. A pair of matched resistors are coupled between the inputs of the differential amplifier and a reference point so that the values of the resistors establish the rail-to-rail operating range of the system. Various resistors at the input of the amplifier enable the data to be determined by differences in the currents in the first and second differential lines and not by the difference between a signal and local ground.
A concrete poured wall corner slab saver and form attachment device that includes a slab saver corner piece having two sides with an inwardly directed central stem portion, and a form attachment device which is a generally shaped triangular form configured to be inserted between one side of corner piece and the stem portion of the corner piece. The form attachment device further a longitudinal aperture near an upper edge that extends through the attachment device with an aperture therein sized to insert a nail for engaging the combined slab saver corner piece and form attachment device to a form board, The attachment device has a generally C-shaped slotted portion forming a slotted aperture configured to engage the expanded portion of the stem of the corner piece and a hollowed core portion to more fully encase the device within the poured concrete.