Datasheet

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DESCRIPTION/ORDERING INFORMATION (CONTINUED)
SN74LVCH16652A
16-BIT BUS TRANSCEIVER AND REGISTER
WITH 3-STATE OUTPUTS
SCAS319I – NOVEMBER 1993 – REVISED MARCH 2005
Complementary output-enable (OEAB and OEBA) inputs control the transceiver functions. Select-control (SAB
and SBA) inputs select whether real-time or stored data is transferred. A low input level selects real-time data,
and a high input level selects stored data. The circuitry used for select control eliminates the typical decoding
glitch that occurs in a multiplexer during the transition between stored and real-time data. Figure 1 illustrates the
four fundamental bus-management functions that can be performed with the SN74LVCH16652A.
Data on the A or B bus, or both, can be stored in the internal D flip-flops by low-to-high transitions at the
appropriate clock (CLKAB or CLKBA) inputs, regardless of the levels on the select-control or output-enable
inputs. When SAB and SBA are in the real-time transfer mode, it also is possible to store data without using the
internal D-type flip-flops by simultaneously enabling OEAB and OEBA. In this configuration, each output
reinforces its input. When all other data sources to the two sets of bus lines are at high impedance, each set of
bus lines remains at its last level configuration.
To ensure the high-impedance state during power up or power down, OEBA should be tied to V
CC
through a
pullup resistor and OEAB should be tied to GND through a pulldown resistor; the minimum value of the resistor is
determined by the current-sinking/current-sourcing capability of the driver.
Inputs can be driven from either 3.3-V or 5-V devices. This feature allows the use of these devices as translators
in a mixed 3.3-V/5-V system environment.
Active bus-hold circuitry is provided to hold unused or floating data inputs at a valid logic level. Use of pullup or
pulldown resistors with the bus-hold circuitry is not recommended. The bus-hold circuitry is part of the input
circuit and is not disabled by OE or DIR.
Table 1. FUNCTION TABLE
INPUTS DATA I/O
(1)
OPERATION OR FUNCTION
OEAB OEBA CLKAB CLKBA SAB SBA A1–A8 B1–B8
L H H or L H or L X X Input Input Isolation
L H ↑ ↑ X X Input Input Store A and B data
X H ↑ H or L X X Input Unspecified
(2)
Store A, hold B
H H ↑ ↑ X
(2)
X Input Output Store A in both registers
L X H or L ↑ X X Unspecified
(2)
Input Hold A, store B
L L ↑ ↑ X X
(2)
Output Input Store B in both registers
L L X X X L Output Input Real-time B data to A bus
L L X H or L X H Output Input Stored B data to A bus
H H X X L X Input Output Real-time A data to B bus
H H H or L X H X Input Output Stored A data to B bus
Stored A data to B bus and
H L H or L H or L H H Output Output
stored B data to A bus
(1) The data-output functions may be enabled or disabled by a variety of level combinations at OEAB or OEBA. Data-input functions always
are enabled; i.e., data at the bus terminals is stored on every low-to-high transition of the clock inputs.
(2) Select control = L; clocks can occur simultaneously.
Select control = H; clocks must be staggered to load both registers.
2