OCTAL TRANSCEIVER WITH PARITY GENERATOR/CHECKER
AND 3ĆSTATE OUTPUTS
SCBS079B − NOVEMBER 1991 − REVISED APRIL 1994
• State-of-the-Art BiCMOS Design
Significantly Reduces ICCZ
• ESD Protection Exceeds 2000 V Per
MIL-STD-883C, Method 3015; Exceeds
200 V Using Machine Model (C = 200 pF,
R = 0)
• 3-State B Outputs Sink 48 mA or 64 mA
and Source 12 mA or 15 mA
• Package Options Include Plastic
Small-Outline (DW) Packages and Standard
Plastic 300-mil DIPs (NT)
The SN74BCT657 contains eight noninverting
transceivers with 3-state outputs and an 8-bit
parity generator/checker. It is intended for bus-
DW OR NT PACKAGE
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 (OE) 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
the parity-select (ODD/EVEN) input 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 as follows:
− Odd and the PARITY input is high, then ERR will be high signifying no error.
− Even and the PARITY input is high, then ERR will be low indicating an error.
The SN74BCT657 is characterized for operation from 0°C to 70°C.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
Copyright 1994, Texas Instruments Incorporated
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