MC145026, MC145027, MC145028 Technical Data, Rev. 4

8

Freescale Semiconductor

Operating Characteristics

3

Operating Characteristics

3.1

MC145026

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 Figure 11).

Each transmitted trinary digit is encoded into pulses (see Figure 12). A logic 0 (low) is encoded as two

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

a high and a low can be forced at an input, an open is assumed and is encoded as such. The “high” and

Figure 5. Output Transition Time

Figure 7. Encoder Clock Frequency

Figure 8. TE Pulse Width

Figure 9. Test Circuit

ANY OUTPUT

10%

90%

10%

90%

50%

50%

TE

DEVICE

UNDER

TEST

OUTPUT

TEST POINT

* Includes all probe and fixture capacitance.