mc145028 Freescale Semiconductor, Inc, mc145028 Datasheet - Page 9

• Manufacturer Part Number: mc145028
• Description: Mc145027 Encoder And Decoder Pair
• Manufacturer: Freescale Semiconductor, Inc

“low” levels are 70% and 30% of the supply voltage as shown in the Electrical Characteristics table. The
weak “output” device sinks/sources up to 110 µA at a 5 V supply level, 500 µA at 10 V, and 1 mA at 15 V.
The TE input has an internal pull-up device so that a simple switch may be used to force the input low.
While TE is high, the encoder is completely disabled, the oscillator is inhibited, and the current drain is
reduced to quiescent current. When TE is brought low, the oscillator is started and the transmit sequence
begins. The inputs are then sequentially selected, and determinations are made as to the input logic states.
This information is serially transmitted via the D
3.2
This decoder receives the serial data from the encoder and outputs the data, if it is valid. The transmitted
data, consisting of two identical words, is examined bit by bit during reception. The first five trinary digits
are assumed to be the address. If the received address matches the local address, the next four (data) bits
are internally stored, but are not transferred to the output data latch. As the second encoded word is
received, the address must again match. If a match occurs, the new data bits are checked against the
previously stored data bits. If the two nibbles of data (four bits each) match, the data is transferred to the
output data latch by VT and remains until new data replaces it. At the same time, the VT output pin is
brought high and remains high until an error is received or until no input signal is received for four data
periods (see
Although the address information may be encoded in trinary, the data information must be either a 1 or 0.
A trinary (open) data line is decoded as a logic 1.
3.3
This decoder operates in the same manner as the MC145027 except that nine address lines are used and
no data output is available. The VT output is used to indicate that a valid address has been received. For
transmission security, two identical transmitted words must be consecutively received before a VT output
signal is issued.
The MC145028 allows 19,683 addresses when trinary levels are used. 512 addresses are possible when
binary levels are used.
4
4.1
A1 - A5, A6/D6 - A9/D9
Address, Address/Data Inputs (Pins 1 - 7, 9, and 10)
These address/data inputs are encoded and the data is sent serially from the encoder via the D
R
(Pins 11, 12, and 13)
These pins are part of the oscillator section of the encoder (see
Freescale Semiconductor
S
, C
TC
Pin Descriptions
, R
MC145027
MC145028
MC145026 Encoder
TC
Figure
11).
MC145026, MC145027, MC145028 Technical Data, Rev. 4
out
pin.
Figure
10).
Pin Descriptions
out
pin.
9