7-Bit Bus Interfaces With 3-State Outputs

The ’ACT1284 devices are designed for asynchronous two-way communication between data buses. The control function minimizes external timing requirements.

The devices allow data transmission in either the A-to-B or the B-to-A direction for bits 1, 2, 3, and 4, depending on the logic level at the direction-control (DIR) input. Bits 5, 6, and 7, however, always transmit in the A-to-B direction.

The output drive for each mode is determined by the high-drive (HD) control pin. When HD is high, the high drive is delivered by the totem-pole configuration, and when HD is low, the outputs are open drain. This meets the drive requirements as specified in the IEEE 1284-I (level-1 type) and the IEEE 1284-II (level-2 type) parallel peripheral-interface specification.