January 1995
Revised January 1999
74ABT16501 18-Bit Universal Bus Transceivers with 3-STATE Outputs
© 1999 Fairchild Semiconductor Corporation DS011690.prf www.fairchildsemi.com
74ABT16501
18-Bit Universal Bus Transceivers with 3-STATE Outputs
General Description
The ABT16501 18-bit universal bus transceiver combines
D-type latches and D-type flip-flops to allow data flow in
transparent, latched, and clocked modes.
Data flow in each direction is controlled by output-enable
(OEAB and OEBA
), latch-enable (LEAB and LEBA), and
clock (CLKAB and CLKBA) inputs. For A-to-B data flow, the
device operates in the transparent mode when LEAB is
HIGH. When LEAB is LOW, the A data is latched if CLKAB
is held at a HIGH or LOW logic level. If LEAB is LOW, the A
bus data is stored in the latch/flip-flop on the LOW-to-HIGH
transition of CLKAB. Output-enable OEAB is active-high.
When OEAB is HIGH, the outputs are active. When OEAB
is LOW, the outputs are in the high-impedance state.
Data flow for B to A is similar to that of A to B but uses
OEBA
, LEBA, and CLKBA. The output enables are com-
plementary (OEAB is active HIGH and OEBA
is active
LOW).
To ensure the high-impedance state during power up or
power down, OE inputs should be tied to GND through a
pulldown resistor; the minimum value of the resistor is
determined by the current-sourcing capability of the driver.
Features
■ Combines D-Type latches and D-Type flip-flops for oper-
ation in transparent, latched, or clocked mode
■ Flow-through architecture optimizes PCB layout
■ Guaranteed latch-up protection
■ High impedance glitch free bus loading during entire
power up and power down cycle
■ Non-destructive hot insertion capability
Ordering Code:
Devices also available in Tape or Reel. Specify by appending the suffix letter “X” to the ordering code.
Connection Diagram
Pin Assignment for SSOP
Function Table (Note 1)
Note 1: A-to-B data flow is shown: B-to-A flow is similar but uses OEBA,
LEBA, and CLKBA.
Note 2: Output level before the indicated steady-state input conditions
were established.
Note 3: Output level before the indicated steady-state input conditions
were established, provided that CLKAB was HIGH before LEAB went LOW.
Order Number Package Number Package Description
74ABT16501CSSC MS56A 56-Lead Shrink Small Outline Package (SSOP), JEDEC MO-118, 0.300” Wide
74ABT16501CMTD MTD56 56-Lead Thin Shrink Small Outline Package (TSSOP), JEDEC MO-153, 6.1mm Wide
Inputs Output
OEAB LEAB CLKAB A B
LXXX Z
HHXL L
HHXH H
HL↑ LL
HL↑ HH
HLHXB
0
(Note 2)
HLLXB
0
(Note 3)
