Wall Mountable Display Solution

4Discovery-50

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13.2. 4Discovery as a Host (DB01 – RS485)

The 4Discovery is capable of being the Master device of the RS485 network. It therefore needs to communicate to

all Slave devices on the network and handle the replies from each of them.

The 4Discovery is fully programmable by the User when used in Designer or ViSi, and therefore every aspect of the

system needs to be managed by User Code. To enable the 4Discovery to transmit out of the RS485, the Turn Around

pin needs to be High, which is controlled using the PA14 GPIO on the Diablo16 processor on board the 4Discovery.

To enable the 4Discovery to receive over RS485, the Turn Around pin needs to be Low.

As mentioned in 11.1 ‘Master and Slaves’, the 4Discovery is capable of being used in new RS485 systems, as well as

existing systems. When used in new systems, the 4Discovery protocol can be more easily customised to provide the

best mix of features and performance as possible, compared to existing systems which typically have a protocol

already defined or devices which use a fixed protocol. The 4Discovery is fully programmable so is capable of working

with a large range of new and existing systems, even if the protocols are specialised. A main factor is that all devices

on the RS485 bus need to take the same protocol, else the system will not operate correctly.

If there are systems which are not capable of determining when the Slaves are ‘allowed’ to Transmit, the Turn

Around pin may be used from the 4Discovery to indicate when the Master (4Discovery) is transmitting or receiving

and may be useful to assist the Slave.

Figure 2. This shows a 4Discovery as the Master of the RS485 Bus, and there are multiple Slaves, which can include

multiple 4Discovery’s (as Slaves). The Master could communicate to each of the Slaves individually, or to all of them

by doing a Broadcast, however this is dictated by the User Protocol and how the system is set up.

Each Device on the bus needs to communicate using the same protocol, and each device needs to be able to control

its own Transmit/Receive mode of its RS485 transceiver.