Impulse 8126 - Manual (Page 36)

8126 TTL Logic & Example Circuits
The 8126 uses 74ABT245 octal bidirectional transceivers to provide TTL
input/output capabilities. Each bit is pulled to +5V through a 10K Ω pull-up resistor
to insure each bit is at a known state when not driven.
The inputs use positive logic and are active true. If an input is driven high (2V to
5.25V) it will read as a logical one (1), and if driven low (0V to 0.8V) it will read as a
logical zero (0). If an input is not driven, it will read as a one (1) due to the 10K Ω
pull-up resistors on each port.
The outputs use negative logic. Writing a zero (0) to an output corresponds to 5V,
while writing a one (1) to an output corresponds to 0V.
© Sealevel Systems, Inc. - 34 - SeaDAC Lite User Manual