)
input is high, both the A and B ports are in the high-impedance
state.SCBS090A - NOVEMBER 1991 - REVISED JANUARY 1994
The SN64BCT657 contains eight noninverting buffers with parity
generator/checker circuits and control signals. The transmit/receive
(T/R\) input determines the direction of data flow. When T/R\ is
high, data flows from the A port to the B port (transmit mode); when
T/R\ is low, data flows from the B port to the A port (receive mode).
When the output-enable ()
input is high, both the A and B ports are in the high-impedance
state.
Odd or even parity is selected by a logic high or low level on the
ODD
input. PARITY
carries the parity bit value; it is an output from the parity
generator/checker in the transmit mode and an input to the parity
generator/checker in the receive mode.
In the transmit mode, after the A bus is polled to determine the
number of high bits, PARITY is set to the logic level that maintains
the parity sense selected by the level at the ODD input. For example, if ODD is low (even parity selected) and
there are five high bits on the A bus, then PARITY is set to the
logic high level so that an even number of the nine total bits (eight
A-bus bits plus parity bit) are high.
In the receive mode, after the B bus is polled to determine the
number of high bits, the error (
) output logic level indicates whether or not the data
to be received exhibits the correct parity sense. For example, if
ODD is high (odd
parity selected), PARITY is high, and there are three high bits on
the B bus, then is low,
indicating a parity error.
The SN64BCT657 is characterized for operation from -40°C to 85°C and 0°C to 70°C.