SN74F657 OCTAL TRANSCEIVER WITH PARITY GENERATOR/CHECKER AND 3-STATE OUTPUTS

SDFS027A - D3217, JANUARY 1989 - REVISED OCTOBER 1993

features

• Combines ´F245 and ´F280B Functions in One Package
• High-Impedance N-P-N Inputs for Reduced Loading (70 uA in Low and High States)
• High Output Drive and Light Bus Loading
• 3-State B Outputs Sink 64 mA and Source 15 mA
• Input Diodes for Termination Effects
• Package Options Include Plastic Small-Outline Packages and Standard Plastic 300-mil DIPs

description

The SN74F657 contains eight noninverting buffers with 3-stateoutputs and an 8-bit parity generator/checker. It is intended forbus-oriented applications. The buffers have a specified currentsinking capability of 24 mA at the A port and 64 mA at the B port.

The transmit/receive (T/R\) input determines the direction of thedata flow through the bidirectional transceivers. When T/R\ is high,data is transmitted from the A port to the B port. When T/R\ is low,data is received at the A port from the B port.

When the output enable ()input is high, both the A and B ports are placed in a high-impedancestate (disabled). The ODD/EVEN\ input allows the user to selectbetween odd or even parity systems. When transmitting from A port toB port (T/R\ high), PARITY is an output from the generator/checker.When receiving from B port to A port (T/R\ low), PARITY is an input.

When transmitting (T/R\ high), the parity select (ODD/EVEN\) inputis made high or low as appropriate. The A port is then polled todetermine the number of high bits.The PARITY output goes to the logicstate determined by ODD/EVEN\ and the number of high bits on A port.When ODD/EVEN\ is low (for even parity) and the number of high bitson A port is odd, the PARITY will be high, transmitting even parity.If the number of high bits on A port is even, the PARITY will be low,keeping even parity.

When in the receive mode (T/R\ low), the B port is polled todetermine the number of high bits. If ODD/EVEN\ is low (for evenparity) and the number of highs on B port is:

1. 1. Odd and the PARITY input is high, then ERR\ will be high signifying no error.
2. 2. Even and the PARITY input is high, then ERR\ will be low indicating an error.

The SN74F657 is characterized for operation from 0°C to70°C.

View more information about generic part numbers:SN74F657

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