directory

1, 2 line -Modus

2, 4 line -Modus

3, 4 wire -Modus and 2 wire -Modus compatibility

4, RS232 – Modus

5, RS485 – Modus

A Modus multi-point serial link system consists of a main cable (trunk) and some possible branch cables, with line terminals at both ends of the trunk cable for impedance matching. The general picture of the serial bus structure in a Modus multi-point serial link system is shown below.

Different devices can run in the same Modus serial links in the system, the integration of communication transceiver equipment through the passive joints and branch cable connected to the trunk (such as from station 1 and host), no integrated communication transceiver equipment through active joints and branch cable connected to the trunk (active joint integrated transceiver) (for example from station 2), The device is connected directly to the trunk cable in a Daisy chain form (for example, slave station N).

A few key names to highlight here:

  • The interfaces between the trunk are called ITr(trunk interface);
  • The interface between the device and the passive connector is called IDv (branch interface).
  • The interface between the device and the active connector is called AUI (Additional unit interface).

1, 2 line -Modus

Modus solutions on serial links should implement a “2-wire” electrical interface in accordance with EIA/TIA-485 standards, where only one driver has the right to send signals at any one time on a 2-wire bus. There is actually a third wire that connects all the devices on the bus to each other: the common ground. The 2-line Modus topology is shown below:

The 2-wire -Modus circuit is defined as follows:

2, 4 line -Modus

The 4-wire Modus device allows 2-bus (4-wire) one-way data transfer. Data on the master bus (RXD1-RxD2) can only be received by the slave, and data on the slave bus (TXD0-TXD1) can only be received by the master. In fact, the common ground as the fifth conductor must connect all devices on the 4-wire bus to each other. 4-wire -Modus devices must implement one driver and one transceiver for each pair of balanced lines in accordance with EIA/TIA-485 (this approach is sometimes referred to as “RS422”, which is incorrect: the RS422 standard does not support several devices on a pair of balanced lines).

In 4-wire Modus, both master and slave stations have IDv interfaces with the same 5 required circuits. As the master station, the following conditions should be met:

  • Since receiving data from slave on the peer bus (TXD1-TXD0);
  • Data is sent on the master pair bus (RXD1-RXD0) and received by the slave station.

The 4-wire-cable system must intersect the two pairs of buses between the ITr and the IDv of the master station, as shown below:

The 4-wire Modus topology is shown below:

The 4-wire Modus circuit is defined as follows:

3, 4 wire -Modus and 2 wire -Modus compatibility

To connect the device performing the 2-wire physical interface to an existing 4-wire system, the 4-wire cable system can be modified as follows:

  • TXD0 signal should be connected with RXD0 signal, so that it becomes D0 signal;
  • TXD1 signal should be connected with TXD0 signal to make it a D1 signal;
  • Pull-up, pull-down resistors and line terminal resistors shall be rearranged to properly accommodate D0, D1 signals.

Example 1: The figure below shows an example of how slave stations 2 and 3 using a 2-wire interface can work with master and slave 1 using a 4-wire interface.

To connect a device performing a 4-wire physical interface to an existing 2-wire system, the 4-wire interface of the new device can be arranged as follows:

On each 4-wire device interface:

  • TXD0 signal should be connected with RXD0 signal, and then connected to the D0 signal line of the trunk;
  • TXD1 signal should be connected with RXD0 signal, and then connected to the D1 signal line of the trunk.

Example 2: The figure below shows an example of how slave stations 2 and 3 using a 4-wire system can work with master and slave 1 using a 2-wire system.

4, RS232 – Modus

Rs232-modus is only used for point-to-point interconnection over short distances (typically less than 20m). Each TXD connects to another device’s RXD for DCE and DTE communication, which must comply with EIA/TIA-232 standards. The rs232-Modus circuit is defined as follows:

5, RS485 – Modus

A maximum of 32 devices are always allowed in the RS485-Modus system. In the absence of Repeaters, rs485-Modus has a trunk cable along which all devices are connected directly (Daisy chain) or via short branching cables. And some devices can run on RS485-Modus serial links with more than 32 devices.