What the 1-of-8 decode means for your address map
The SN74AHC138DR is a 1-of-8 decoder/demultiplexer from TI's 74AHC family — three address inputs select one of eight active-low outputs. That 1 x 3:8 configuration maps directly to memory-mapped I/O or register-select buses where three address lines need to enable one of eight peripheral chip-selects.
Output drive and temperature grade — the design-in limits
Each output sources or sinks 8 mA — enough to drive a standard TTL input or an LED indicator directly, but not a high-fan-out bus without buffering.