SN74ALS870

This SN74ALS870 device features two 16-word by 4-bit register files. Each SN74ALS870 register file has individual write-enable (1W, 2W) controls and address lines. This device has two 4-bit data I/O ports (DQA1DQA4 and DQB1DQB4). The data I/O ports can output to bus A and bus B, receive input from bus A and bus B, receive input from bus A and output to bus B, or output to bus A and receive input from bus B. To prevent writing conflicts in the dual-input mode, the B-input port takes priority. Two select (S0 and S1) lines control which port has access to which register. S2 determines whether the A ports are in the input or the output modes and S3 does likewise for the B ports. The address lines (1A01A3 or 2A02A3) are decoded by an internal 1-of-16 decoder to select which register word is to be accessed. All outputs are 3-state buffer-type outputs designed specifically to drive bus lines directly.

The SN74ALS870 is characterized for operation from 0°C to 70°C.