FCT Interface Logic, Octal Bus Transceivers/ Registers, Open Drain (A Side), Three-State (B Side)The CD74FCT653 and CD74FCT654 octal bus transceiv-
ers Registers use a small geometry BiCMOS technology. The
output stage is a combination of bipolar and CMOS Transistors
that limits the output HIGH level to two Diode drops below VCC.
This resultant lowering of output swing (0V to 3.7V) reduces
power bus ringing (a source of EMI) and minimizes VCC
bounce and ground bounce and their effects during simulta-
neous output switching. The output configuration also
enhances switching speed and is capable of sinking 64mA.
The CD74FCT653 is an inverting type having open drains on
the A output and three state outputs on the B side. The
CD74FCT654 differs only in that it is a noninverting type. These
devices consist of Bus Transceiver circuits, D-Type Flip-Flops and
control circuitry arranged for multiplexed transmission of data
directly from the data bus or from the internal storage Registers
Output Enables OEAB and OEBA are provided to control the
transceiver functions. SAB and SBA control pins are provided
to select whether real-time or stored data is transferred. The cir-
cuitry used for select control will eliminate the typical decoding
glitch that occurs in a multiplexer during the transition between
stored and real-time data. A LOW input level selects real-time
data and a HIGH selects stored data. The following examples
demonstrate the four fundamental bus management functions
that CAN be performed with the octal Bus Transceivers and regis-
ters. By Texas Instruments
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