What the 1-of-8 decoding means for your address bus
The SN74HC138DBR is a single 3-to-8 line decoder/demultiplexer from TI's 74HC family — it takes a 3-bit binary address on its select inputs and asserts one of eight active-low outputs. The single independent circuit (1 x 3:8) means the part handles one address decode path per package, with the demultiplexer mode letting you route a data input to one of eight outputs by holding the address lines.
Output drive and package — what the 5.2 mA rating tells you
Each output sources or sinks 5.2 mA (both high and low), which is typical for HC logic — enough to drive a few CMOS gate inputs or a low-power LED indicator, but not a relay coil or a long backplane trace without a buffer. The 74HC series uses a standard CMOS process with high noise immunity and symmetrical drive — the 5.2 mA figure is the same for sourcing and sinking, so the output high and low voltage drops are balanced. That matters when the downstream logic has tight VIH/VIL thresholds.