3
18
Series of Decoders
Functional Description
Operation
Flowchart
18
The 3 series of decoders provides various com-
binations of address and data pins in different
packages. It is paired with the 3
18
series of
encoders. The decoders receive data transmit-
ted by the encoders and interpret the first N
bits of the code period as address and the last
18–N bits as data (where N is the address code
number). A signal on the DIN pin then activates
the oscillator which in turns decodes the incom-
ing address and data. The decoders will check
the received address twice continuously. If all
the received address codes match the contents
of the decoder’s local address, the 18–N bits of
data are decoded to activate the output pins,
and the VT pin is set high to indicate a valid
transmission. That will last until the address
code is incorrect or no signal has been received.
The output of the VT pin is high only when the
transmission is valid. Otherwise it is low al-
ways.
Output type
There are 2 types of output to select from:
•
Momentary type
The data outputs follow the encoder during a
valid transmission and then reset.
•
Latch type
The data outputs follow the encoder during a
valid transmission, and are then latched in
this state until the next valid transmission
occurs.
Note: The oscillator is disabled in the
standby state and activated as long as
a logic “high” signal is applied to the
DIN pin. i.e., the DIN should be kept
“low” if there is no signal input.
5
2nd Oct ’97
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
