74AC257 74ACT257 Quad 2-Input Multiplexer with 3-STATE Outputs November 1988 Revised November 1999 74AC257 74ACT257 Quad 2-Input Multiplexer with 3-STATE Outputs General Description Features The AC/ACT257 is a quad 2-input multiplexer with 3- I and I reduced by 50% CC OZ STATE outputs. Four bits of data from two sources can be Multiplexer expansion by tying outputs together selected using a Common Data Select input. The four out- Noninverting 3-STATE outputs puts present the selected data in true (noninverted) form. Outputs source/sink 24 mA The outputs may be switched to a high impedance state by placing a logic HIGH on the common Output Enable (OE) ACT257 has TTL-compatible inputs input, allowing the outputs to interface directly with bus-ori- ented systems. Ordering Code: Order Number Package Number Package Description 74AC257SC M16A 16-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-012, 0.150 Narrow Body 74AC257SJ M16D 16-Lead Small Outline Package (SOP), EIAJ TYPE II, 5.3mm Wide 74AC257MTC MTC16 16-Lead Thin Shrink Small Outline Package (TSSOP), JEDEC MO-153, 4.4mm Wide 74AC257PC N16E 16-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300 Wide 74ACT257SC M16A 16-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-012, 0.150 Narrow Body 74ACT257SJ M16D 16-Lead Small Outline Package (SOP), EIAJ TYPE II, 5.3mm Wide 74ACT257MTC MTC16 16-Lead Thin Shrink Small Outline Package (TSSOP), JEDEC MO-153, 4.4mm Wide 74ACT257PC N16E 16-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300 Wide Device also available in Tape and Reel. Specify by appending suffix letter X to the ordering code. Logic Symbols Connection Diagram IEEE/IEC Pin Descriptions Pin Names Description S Common Data Select Input OE 3-STATE Output Enable Input I I Data Inputs from Source 0 0a 0d I I Data Inputs from Source 1 1a 1d Z Z 3-STATE Multiplexer Outputs a d FACT is a trademark of Fairchild Semiconductor Corporation. 1999 Fairchild Semiconductor Corporation DS009949 www.fairchildsemi.comFunctional Description Truth Table The AC/ACT257 is quad 2-input multiplexer with 3-STATE Output Select Data Outputs outputs. It selects four bits of data from two sources under control of a Common Data Select input. When the Select Enable Input Inputs input is LOW, the I inputs are selected and when Select 0x OE SI I Z is HIGH, the I inputs are selected. The data on the 0 1 1x selected inputs appears at the outputs in true (noninverted) HX X X Z form. The device is the logic implementation of a 4-pole, 2- LH X L L position switch where the position of the switch is deter- mined by the logic levels supplied to the Select input. The LH X H H logic equations for the outputs are as follows: LL L X L Z = OE (1 S + I S) a 1a 0a LL H X H Z = OE (1 S + I S) b 1b 0b Z = OE (1 S + I S) H = HIGH Voltage Level c 1c 0c L = LOW Voltage Level Z = OE (1 S + I S) d 1d 0d X = Immaterial Z = High Impedance When the Output Enable (OE) is HIGH, the outputs are forced to a high impedance state. If the outputs are tied together, all but one device must be in the high impedance state to avoid high currents that would exceed the maxi- mum ratings. Designers should ensure the Output Enable signals to 3-STATE devices whose outputs are tied together are designed so there is no overlap. Logic Diagram Please note that this diagram is provided only for the understanding of logic operations and should not be used to estimate propagation delays. www.fairchildsemi.com 2 74AC257 74ACT257