74GTL1655A datasheet(2/16 Pages) STMICROELECTRONICS

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74GTL1655A

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controlled by output-enable (OEAB and OEBA),

latch-enable (LEAB and LEBA), and clock (CLK)

inputs. For A-to-B data flow, the devices operate

in the transparent mode when LEAB is high. When

LEAB is low, the A data is latched if CLK is held at

a high or low logic level. If LEAB is low, the A data

is stored in the latch/flip-flop on the low-to-high

transition of CLK. When OEAB is low, the outputs

are active. When OEAB is high, 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 CLK. The output enable (OE) is used to

disable both ports simultaneously.

Active bus-hold circuitry is provided on the A port

to hold unused or floating data inputs at a valid

logic level. When VCC is between 0 and 1.5 V, the

device is in the high-impedance state during

power up or power down. However, to ensure the

high-impedance state above 1.5V, OE should be

tied to VCC through a pull-up resistor; the

minimum value of the resistor is determined by the

current-sinking capability of the driver.

All input and output are equipped with protection

circuits against static discharge, giving them 2KV

ESD immunity and transient excess voltage.

Figure 2: Input And Output Equivalent Circuit

Table 2: Pin Description

PIN N°

SYMBOL

NAME AND FUNCTION

1, 2

1OEAB, 1OEBA

Output Enable Input

4, 6, 7, 9, 11, 13, 14, 16

1A1 to 1A8

Data Inputs/Outputs LVTTL

17, 19, 20, 22, 23, 25, 27, 29

2A1 to 2A8

Data Inputs/Outputs LVTTL

31, 32

2OEAB, 2OEBA

Output Enable Input

34, 35

2LEBA, 2LEAB

Latch Enable

BIAS VCC

Pre-Charge Supply Voltage

37, 38, 40, 42, 43, 45, 46, 48

2B8 to 2B1

Data Inputs/Outputs GTL/GTL+

VREF

GTL Voltage Reference Input

49, 51, 52, 54, 55, 56, 58, 59

2A1 to 2A8

Data Inputs/Outputs GTL/GTL+

VERC

Edge Rate Control

62, 63

1LEBA, 1LEAB

Latch Enable

CLK

Clock Input (LOW to HIGH edge triggered)

5, 8, 10, 12, 18, 21, 24, 26, 30,

39, 44, 47, 53, 57, 60

GND

Ground (0V)

3, 15, 28, 50

VCC

Positive Supply Voltage

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