EPC120 EPC [Espros Photonics corp], EPC120 Datasheet - Page 8

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

4. 2-Wire Bus
2 Dependent on the electro-mechanical design and the bus location of the edge, the termination network can be necessary. It is in the
3 The effective length is dependent on the electro-mechanical design of the edge. The values in the table are indicative only.
The 2-wire bus and the power supply utilize the same two wires. The data is transmitted by modulating the current on the power-line. The
modulated current, together with the resistor in the power supply, produce a voltage signal on the line. All devices receive this signal. The
system is designed to operate with a line impedance of 50Ω (±5%). An inductor in parallel of the resistor or a DC regulator with a lowpass
feedback shape the pulses and keep the the DC voltage drop over the resistor low. The required corner frequency of this L/R-filter is listed in
the table below.
The communication interface has been designed to be used for line lengths of up to 100m and with up to 1023 sensor devices. For line
lengths of up to 3m it is possible to operate the line without termination
(±5%) which is equal to the line impedance and a capacitor of 100nF in series.
The data rate on the 2-wire bus is set by the parameter DRATE. It also defines T
page Error: Reference source not found) and the required inductor according to Table 1. The maximum data rate allowed on the 2-wire bis is
depending on the bus length. The longer the bus wire, the lower the data rate. Table 1 shows the possible bus wire length according to the
data rate.
The default value of DRATE is 00. The parameter DRATE has to be identical for all devices on one physical 2-wire bus.
The SPI bus should be faster than the 2-wire bus, otherwise the communication does not work. Since the command length dependent on the
command type, the delay time to the next command has to be adjusted to the previous command. The time delay can be calculated with the
given data length in Table 7 on page 19.
The parameter CDET defines the optimal signal amplitude for the receiver. The maximum rate at pin VDDR (5.5V) should not be exceeded
and signals which are smaller than 70% of the recommended values are not detected.
Since the command length is dependent on the command type, the delay time to the next command has to be adjusted to the previous
command. The time delay can be calculated with the given data length in Table 7 on page 19. The data handling chain of the 2-wire
communication channel is shown in Figure 6.
© 2011 ESPROS Photonics Corporation
Characteristics subject to change without notice
responsibility of the system designer that the data integrity on the bus is guaranteed. Data integrity can be tested by readout bus
transmission errors. It is strongly recommended to do that during type qualification during EMI qualification tests .
DRATE
00
01
10
11
k
8
4
2
1
Command
Transmitter
Data Rate on the
Manchester
Parity Bits
Message
2-Wire Bus
Encoder
Original
Current
added
250 kbit/s
500 kbit/s
1 Mbit/s
2 Mbit/s
Sink
Table 1: Data rate of the 2-wire communication
Data
Figure 6: Data handling
Minimal Data Rate
Required on SPI
300 kbit/s
600 kbit/s
1.2 Mbit/s
2.4 Mbit/s
Interface
Filter
Line
8
2
. Above this length the line has to be terminated by a resistor of 50 Ω
SCANmin
Frequency L/R
(refer to Chapter Error: Reference source not found on
Command
0.5 MHz
Corner
1 MHz
2 MHz
4 MHz
Error Correction
Error Detection
Receiver
Manchester
Decoder +
Converter
Received
Message
A/D
Inductor
16µH
Data
8µH
4µH
2µH
Datasheet epc12x - V2.1
12 … 100m
Bus Wire
6 … 12m
Length
3 … 6m
≤ 3m
www.espros.ch
epc120
3