mc145028 Freescale Semiconductor, Inc, mc145028 Datasheet - Page 8

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

Operating Characteristics
3
3.1
The encoder serially transmits trinary data as defined by the state of the A1 - A5 and A6/D6 - A9/D9 input
pins. These pins may be in either of three states (low, high, or open) allowing 19,683 possible codes. The
transmit sequence is initiated by a low level on the TE input pin. Upon power-up, the MC145026 can
continuously transmit as long as TE remains low (also, the device can transmit two-word sequences by
pulsing TE low). However, no MC145026 application should be designed to rely upon the first data word
transmitted immediately after power-up because this word may be invalid. Between the two data words,
no signal is sent for three data periods (see
Each transmitted trinary digit is encoded into pulses (see
consecutive short pulses, a logic 1 (high) as two consecutive long pulses, and an open (high impedance)
as a long pulse followed by a short pulse. The input state is determined by using a weak “output” device
to try to force each input high then low. If only a high state results from the two tests, the input is assumed
to be hardwired to V
a high and a low can be forced at an input, an open is assumed and is encoded as such. The “high” and
8
ANY OUTPUT
R
Operating Characteristics
TC
Figure 7. Encoder Clock Frequency
MC145026
Figure 5. Output Transition Time
10%
50%
90%
DD
. If only a low state is obtained, the input is assumed to be hardwired to V
t/f
OSC
t
TLH
MC145026, MC145027, MC145028 Technical Data, Rev. 4
t
THL
* Includes all probe and fixture capacitance.
DEVICE
UNDER
Figure 9. Test Circuit
TEST
Figure
11).
OUTPUT
D
Figure
TEST POINT
in
TE
90%
10%
Figure 6. D
12). A logic 0 (low) is encoded as two
C
Figure 8. TE Pulse Width
L
*
t
f
in
50%
Rise and Fall Time
t
W
t
f
Freescale Semiconductor
V
V
DD
SS
V
V
SS
DD
SS
. If both