1

2

3

4

5

6

7

8

9

10

11

12

24

23

22

21

20

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17

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14

13

T/R

A1

A2

A3

A4

A5

A6

A7

A8

ODD/EVEN

ERR

OE

B1

B2

B3

B4

GND

GND

B5

B6

B7

B8

PARITY

DW OR NT PACKAGE

(TOP VIEW)

SN74BCT657

OCTAL TRANSCEIVER WITH PARITY GENERATOR/CHECKER

AND 3STATE OUTPUTS

SCBS079B − NOVEMBER 1991 − REVISED APRIL 1994

Copyright

2−1

POST OFFICE BOX 655303

POST OFFICE BOX 1443

MIL-STD-883C, Method 3015; Exceeds

200 V Using Machine Model (C = 200 pF,

R = 0)

and Source 12 mA or 15 mA

Small-Outline (DW) Packages and Standard

Plastic 300-mil DIPs (NT)

description

The SN74BCT657 contains eight noninverting

transceivers with 3-state outputs and an 8-bit

parity generator/checker. It is intended for bus-

oriented applications.

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.