epc120
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.
Normal Command
A
0
A
1
A
2
A
3
A
4
A
5
A
6
A
7
A
8
A
9
C
0
C
1
C
2
P
0
P
1
P
2
P
3
P
4
P
5
P
6
P
7
P
8
P
9
Device Address
Command
Parity Bits
Write Command
A
0
A
1
A
2
A
8
A
9
C
0
C
1
C
2
P
0
P
1
Command
P
8
P
9
R
0
R
1
R
2
R
3
R
4
D
0
D
1
Register
D
14
D
15
P
0
P
1
P
8
P
9
Device Address
Parity Bits
Data
Parity Bits
Results
D
0
D
1
D
9
D
10
A
0
A
1
A
2
A
8
A
9
P
0
P
1
P
8
P
9
Data
Device Address
Parity Bits
Register Readout
R
0
R
1
R
2
R
3
R
4
D
0
D
1
Register
D
14
D
15
P
0
P
1
P
8
P
9
Data
Parity Bits
Figure 7: Message Structure
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.
120
Impedance [Ohm]
100
80
60
40
20
0
1.0
1.8
3.2
5.6 10.0 17.8 31.6 56.2 100.0
Pitch [cm]
Figure 8: Line impedance as a function of the element pitch
on a 100 Ohm twisted pair cable
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.
100nF
R
T
Figure 9: Bus termination network
© 2011 ESPROS Photonics Corporation
Characteristics subject to change without notice
9
Datasheet epc12x - V2.1
www.espros.ch
EPC [ ESPROS PHOTONICS CORP ]
