Linx Technologies LICAL-EDC-DS - Manual (Page 7)

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Holtek Data and Packet Structure
The Holtek ® encoders and decoders have tri-state input lines. They
recognize three distinct states: one, zero and open. A one bit is set when
the line is at V
CC
. A zero bit is set when the line is at ground. An open bit is
set when the line is not connected or floating.
The Holtek ® encoders and decoders use a pattern of two logic high pulses
and two logic low pulses for each bit. Two of the pulses are double sized
and the pattern indicates the type of bit. This is shown in Figure 8.
Each data packet consists of 6-bit pilot period (logic low), 2-bit SYNC
period, and 18-bit code period, as shown in Figure 9.
Power On
Is the
E/D_SEL line
high?
Is TE high? Sleep
Wake on Interrupt
Assemble packet
Output packet 3
times
Make pins D0-D7
inputs
Make pins D0-D7
outputs
Valid data
received?
Sleep
Wake on interrupt
Activate outputs
and VT
Address
match?
2nd packet
received?
Data match
previous data?
Clear outputs and
VT
Is DIN high?
Is P_SEL high?
Set protocol to
Holtek
Set protocol to
Serial
Is P_SEL high?
Set protocol to
Holtek
Set protocol to
Serial
Read Data and
Address lines
Assemble packet
Output packet
Read Data and
Address lines Valid data
received?
Activate outputs
and VT
Address
match?
2nd packet
received?
130ms
timeout?
Reset 130ms timer
1 st valid
packet?
1 st valid
packet?
Assemble inverted
packet
Output packet
Read Data and
Address lines
Encoder Decoder
YES
NO
YES
NO
YES
NO
NO
NO
YES
YES
YES
NO
NO YES NO YES
NO YES
YES
NO
YES
NO
NO
YES
YES
NO
NO
YES
NO
YES
Figure 7: DS Series Encoder/Decoder Flowchart
Pilot Period
(6 bits)
1/6 bit
Sync. Period Address Code Period Data Code Period
fosc/33
One
Zero
Open
Figure 8: Holtek ® Protocol Input Interpretation
Figure 9: Holtek ® Protocol Packet Structure