Packaging information
| Package | Pins SOIC (DW) | 24 |
| Operating temperature range (°C) 0 to 70 |
| Package qty | Carrier 25 | TUBE |
Features for the SN74F657
- 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 for the SN74F657
The SN74F657 contains eight noninverting buffers with 3-state outputs and an 8-bit parity generator/checker. It is intended for bus-oriented applications. The buffers have a specified current sinking 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 the data 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-impedance
state (disabled). The ODD/EVEN\ input allows the user to select
between odd or even parity systems. When transmitting from A port to
B 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\) input is made high or low as appropriate. The A port is then polled to determine the number of high bits.The PARITY output goes to the logic state 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 bits on 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 to determine the number of high bits. If ODD/EVEN\ is low (for even parity) and the number of highs on B port is:
- 1. Odd and the PARITY input is high, then ERR\ will be high signifying no error.
- 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 to 70°C.