EPC120 EPC [Espros Photonics corp], EPC120 Datasheet - Page 9

• Manufacturer Part Number: EPC120
• Description: Fully integrated Light-Barrier Chips with 2-Wire Bus Interface
• Manufacturer: EPC [Espros Photonics corp]

Figure 7 shows the different messages with the parity bits. From the interface to the sensor/transmitter device the “normal command” is used
except for the register write command. In the other direction only the register readout has a different format. Notice the different start bits
which identify the direction of the transmission: 00 for the direction interface to sensor devices and 01 in the other direction. Between the
telegrams, an idle time of 2 clock periods are need to detect the start of the transmission.
Bus Wire Considerations
The electromechanical design of a system using multiple epc10x devices on a twisted pair cable with an impedance of typically 100 Ohms has
an impact on the overall impedance of the system. Figure 8 shows the change of the cable impedance with smaller element pitch.
It is highly recommended to terminate the bus line on both sides with an AC terminator network (shown in Figure 9) which matches the overall
impedance of the system according to Figure 8. In order to avoid high DC currents in the termination resistor, a capacitor of 100nF should be
connected in series to the termination resistor.
© 2011 ESPROS Photonics Corporation
Characteristics subject to change without notice
Normal Command
Write Command
Results
Register Readout
Figure 8: Line impedance as a function of the element pitch
D
R
A
A
Device Address
0
0
0
0
A
A
D
R
Register
Data
1
1
1
1
120
100
80
60
40
20
A
A
R
Device Address
0
2
2
2
D
1.0
9
A
R
3
D
3
A
on a 100 Ohm twisted pair cable
1 0
8
R
A
Figure 7: Message Structure
Figure 9: Bus termination network
1.8
4
4
A
A
Device Address
9
0
A
D
Command
5
C
0
A
0
1
A
D
3.2
Data
6
1
C
A
100nF
1
2
A
D
7
C
5.6 10.0 17.8 31.6 56.2 100.0
1 4
Pitch [cm]
2
A
A
D
8
8
P
9
1 5
0
A
A
Parity Bits
9
9
P
P
Command
1
0
C
P
Parity Bits
R
0
0
P
Parity Bits
T
1
C
P
P
1
8
1
C
P
P
9
8
2
P
8
R
P
P
0
0
9
P
9
P
R
Register
1
1
P
R
2
2
R
P
Parity Bits
3
3
R
P
4
4
P
D
5
0
P
D
6
Data
1
P
D
7
1 4
P
D
8
Datasheet epc12x - V2.1
1 5
P
9
P
0
Parity Bits
P
1
www.espros.ch
P
8
epc120
P
9