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September 1993
2
Philips Semiconductors
Product specication
Octal bus transceiver/register; 3-state
74HC/HCT646
FEATURES
Independent register for A and B buses
Multiplexed real-time and stored data
Output capability: bus driver
ICC category: MSI
GENERAL DESCRIPTION
The 74HC/HCT646 are high-speed Si-gate CMOS devices
and are pin compatible with low power Schottky TTL
(LSTTL). They are specified in compliance with JEDEC
standard no. 7A.
The 74HC/HCT646 consist of bus transceiver circuits with
3-state outputs, D-type flip-flops, and control circuitry
arranged for multiplexed transmission of data directly from
the internal registers. Data on the “A” or “B” bus will be
clocked into the registers as the appropriate clock
(CPAB and CPBA) goes to a HIGH logic level. Output
enable (OE) and direction (DIR) inputs are provided to
control the transceiver function. In the transceiver mode,
data present at the high-impedance port may be stored in
either the “A” or “B” register, or in both. The select source
inputs (SAB and SBA) can multiplex stored and real-time
(transparent mode) data. The direction (DIR) input
determines which bus will receive data when OE is active
(LOW). In the isolation mode (OE = HIGH), “A” data may
be stored in the “B” register and/or “B” data may be stored
in the “A” register.
When an output function is disabled, the input function is
still enabled and may be used to store and transmit data.
Only one of the two buses, A or B, may be driven at a time.
The “646” is functionally identical to the “648”, but has
non-inverting data paths.
QUICK REFERENCE DATA
GND = 0 V; Tamb =25 °C; tr =tf = 6 ns
Notes
1. CPD is used to determine the dynamic power dissipation (PD in W):
PD =CPD × VCC2 × fi + ∑ (CL × VCC2 × fo) where:
fi = input frequency in MHz
fo = output frequency in MHz
∑ (CL × VCC2 × fo) = sum of outputs
CL = output load capacitance in pF
VCC = supply voltage in V
2. For HC the condition is VI = GND to VCC
For HCT the condition is VI = GND to VCC 1.5 V
ORDERING INFORMATION
See
“74HC/HCT/HCU/HCMOS Logic Package Information”.
SYMBOL
PARAMETER
CONDITIONS
TYPICAL
UNIT
HC
HCT
tPHL/ tPLH
propagation delay
An, Bn to Bn, An
CL = 15 pF; VCC =5V
11
13
ns
fmax
maximum clock frequency
69
85
MHz
CI
input capacitance
3.5
pF
CPD
power dissipation capacitance per channel
notes 1 and 2
30
33
pF